diff --git a/services/search/mod.rs b/services/search/mod.rs
new file mode 100644
index 0000000..300bc75
--- /dev/null
+++ b/services/search/mod.rs
@@ -0,0 +1,10 @@
+pub mod service;
+pub mod types;
+
+pub use service::{MerchantIndex, PaymentIndex, RefundIndex, SearchService};
+pub use types::{
+    MerchantPage, MerchantRecord, MerchantSearchQuery, MerchantSortField,
+    PaymentPage, PaymentRecord, PaymentSearchQuery, PaymentSortField, PaymentStatusFilter,
+    RefundPage, RefundRecord, RefundSearchQuery, RefundSortField,
+    SortOrder,
+};
diff --git a/services/search/service.rs b/services/search/service.rs
new file mode 100644
index 0000000..c62232e
--- /dev/null
+++ b/services/search/service.rs
@@ -0,0 +1,276 @@
+/// Advanced Search & Filtering Service — Issue #275
+///
+/// Provides cursor-based paginated search across payments, merchants, and refunds
+/// with multi-field sorting and combined filter support.
+
+use crate::types::{
+    MerchantPage, MerchantRecord, MerchantSearchQuery, MerchantSortField,
+    PaymentPage, PaymentRecord, PaymentSearchQuery, PaymentSortField,
+    RefundPage, RefundRecord, RefundSearchQuery, RefundSortField,
+    SortOrder,
+};
+
+pub const DEFAULT_PAGE_LIMIT: u32 = 20;
+pub const MAX_PAGE_LIMIT: u32 = 100;
+
+// ── Repository traits ─────────────────────────────────────────────────────────
+
+pub trait PaymentIndex: Send + Sync {
+    /// Return all payment records (implementations should use DB indexes).
+    fn all(&self) -> Vec<PaymentRecord>;
+}
+
+pub trait MerchantIndex: Send + Sync {
+    fn all(&self) -> Vec<MerchantRecord>;
+}
+
+pub trait RefundIndex: Send + Sync {
+    fn all(&self) -> Vec<RefundRecord>;
+}
+
+// ── Search service ────────────────────────────────────────────────────────────
+
+pub struct SearchService<P, M, R>
+where
+    P: PaymentIndex,
+    M: MerchantIndex,
+    R: RefundIndex,
+{
+    payments: P,
+    merchants: M,
+    refunds: R,
+}
+
+impl<P: PaymentIndex, M: MerchantIndex, R: RefundIndex> SearchService<P, M, R> {
+    pub fn new(payments: P, merchants: M, refunds: R) -> Self {
+        Self { payments, merchants, refunds }
+    }
+
+    // ── Payments ──────────────────────────────────────────────────────────────
+
+    pub fn search_payments(&self, q: PaymentSearchQuery) -> PaymentPage {
+        let limit = q.limit.unwrap_or(DEFAULT_PAGE_LIMIT).min(MAX_PAGE_LIMIT) as usize;
+
+        let mut records: Vec<PaymentRecord> = self
+            .payments
+            .all()
+            .into_iter()
+            .filter(|r| {
+                if let Some(ref a) = q.merchant_address {
+                    if !r.merchant_address.eq_ignore_ascii_case(a) { return false; }
+                }
+                if let Some(ref a) = q.payer_address {
+                    if !r.payer_address.eq_ignore_ascii_case(a) { return false; }
+                }
+                if let Some(ref t) = q.token_address {
+                    if !r.token_address.eq_ignore_ascii_case(t) { return false; }
+                }
+                if let Some(min) = q.amount_min { if r.amount < min { return false; } }
+                if let Some(max) = q.amount_max { if r.amount > max { return false; } }
+                if let Some(start) = q.date_start { if r.paid_at < start { return false; } }
+                if let Some(end) = q.date_end   { if r.paid_at > end   { return false; } }
+                if let Some(ref statuses) = q.statuses {
+                    let matched = statuses.iter().any(|s| format!("{:?}", s) == r.status);
+                    if !matched { return false; }
+                }
+                true
+            })
+            .collect();
+
+        // Multi-field sort
+        let sort_field = q.sort_field.unwrap_or(PaymentSortField::Date);
+        let asc = q.sort_order.as_ref().map_or(false, |o| *o == SortOrder::Ascending);
+        records.sort_by(|a, b| {
+            let ord = match sort_field {
+                PaymentSortField::Date            => a.paid_at.cmp(&b.paid_at),
+                PaymentSortField::Amount          => a.amount.cmp(&b.amount),
+                PaymentSortField::MerchantAddress => a.merchant_address.cmp(&b.merchant_address),
+                PaymentSortField::PayerAddress    => a.payer_address.cmp(&b.payer_address),
+            };
+            if asc { ord } else { ord.reverse() }
+        });
+
+        let total = records.len() as u64;
+        let (records, next_cursor) = paginate(records, q.cursor.as_deref(), limit, |r| r.order_id.clone());
+        PaymentPage { records, next_cursor, total }
+    }
+
+    // ── Merchants ─────────────────────────────────────────────────────────────
+
+    pub fn search_merchants(&self, q: MerchantSearchQuery) -> MerchantPage {
+        let limit = q.limit.unwrap_or(DEFAULT_PAGE_LIMIT).min(MAX_PAGE_LIMIT) as usize;
+
+        let mut records: Vec<MerchantRecord> = self
+            .merchants
+            .all()
+            .into_iter()
+            .filter(|r| {
+                if let Some(ref name) = q.name_contains {
+                    if !r.name.to_lowercase().contains(&name.to_lowercase()) { return false; }
+                }
+                if let Some(ref cat) = q.category {
+                    if !r.category.eq_ignore_ascii_case(cat) { return false; }
+                }
+                if let Some(active) = q.active { if r.active != active { return false; } }
+                if let Some(wl)     = q.whitelisted { if r.whitelisted != wl { return false; } }
+                true
+            })
+            .collect();
+
+        let sort_field = q.sort_field.unwrap_or(MerchantSortField::Name);
+        let asc = q.sort_order.as_ref().map_or(true, |o| *o == SortOrder::Ascending);
+        records.sort_by(|a, b| {
+            let ord = match sort_field {
+                MerchantSortField::Name         => a.name.cmp(&b.name),
+                MerchantSortField::RegisteredAt => a.registered_at.cmp(&b.registered_at),
+                MerchantSortField::Category     => a.category.cmp(&b.category),
+            };
+            if asc { ord } else { ord.reverse() }
+        });
+
+        let total = records.len() as u64;
+        let (records, next_cursor) = paginate(records, q.cursor.as_deref(), limit, |r| r.address.clone());
+        MerchantPage { records, next_cursor, total }
+    }
+
+    // ── Refunds ───────────────────────────────────────────────────────────────
+
+    pub fn search_refunds(&self, q: RefundSearchQuery) -> RefundPage {
+        let limit = q.limit.unwrap_or(DEFAULT_PAGE_LIMIT).min(MAX_PAGE_LIMIT) as usize;
+
+        let mut records: Vec<RefundRecord> = self
+            .refunds
+            .all()
+            .into_iter()
+            .filter(|r| {
+                if let Some(ref oid) = q.order_id { if r.order_id != *oid { return false; } }
+                if let Some(ref by) = q.initiated_by { if !r.initiated_by.eq_ignore_ascii_case(by) { return false; } }
+                if let Some(ref statuses) = q.statuses {
+                    if !statuses.iter().any(|s| s.eq_ignore_ascii_case(&r.status)) { return false; }
+                }
+                if let Some(min) = q.amount_min { if r.amount < min { return false; } }
+                if let Some(max) = q.amount_max { if r.amount > max { return false; } }
+                if let Some(start) = q.date_start { if r.initiated_at < start { return false; } }
+                if let Some(end)   = q.date_end   { if r.initiated_at > end   { return false; } }
+                true
+            })
+            .collect();
+
+        let sort_field = q.sort_field.unwrap_or(RefundSortField::InitiatedAt);
+        let asc = q.sort_order.as_ref().map_or(false, |o| *o == SortOrder::Ascending);
+        records.sort_by(|a, b| {
+            let ord = match sort_field {
+                RefundSortField::InitiatedAt => a.initiated_at.cmp(&b.initiated_at),
+                RefundSortField::Amount      => a.amount.cmp(&b.amount),
+            };
+            if asc { ord } else { ord.reverse() }
+        });
+
+        let total = records.len() as u64;
+        let (records, next_cursor) = paginate(records, q.cursor.as_deref(), limit, |r| r.refund_id.clone());
+        RefundPage { records, next_cursor, total }
+    }
+}
+
+// ── Cursor-based pagination ───────────────────────────────────────────────────
+
+/// Slices `items` starting after the item whose key matches `cursor`.
+/// Returns (page_items, next_cursor).
+fn paginate<T, F>(items: Vec<T>, cursor: Option<&str>, limit: usize, key_fn: F) -> (Vec<T>, Option<String>)
+where
+    F: Fn(&T) -> String,
+{
+    let start = match cursor {
+        None => 0,
+        Some(c) => items.iter().position(|i| key_fn(i) == c).map_or(0, |p| p + 1),
+    };
+    let slice: Vec<T> = items.into_iter().skip(start).take(limit + 1).collect();
+    if slice.len() > limit {
+        let mut page = slice;
+        let extra = page.pop().unwrap();
+        let next = key_fn(&extra);
+        (page, Some(next))
+    } else {
+        (slice, None)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn payments() -> Vec<PaymentRecord> {
+        vec![
+            PaymentRecord { order_id: "P1".into(), merchant_address: "M1".into(), payer_address: "A1".into(), token_address: "T1".into(), amount: 500, refunded_amount: 0, status: "Completed".into(), paid_at: 1000 },
+            PaymentRecord { order_id: "P2".into(), merchant_address: "M2".into(), payer_address: "A2".into(), token_address: "T1".into(), amount: 200, refunded_amount: 0, status: "Completed".into(), paid_at: 2000 },
+            PaymentRecord { order_id: "P3".into(), merchant_address: "M1".into(), payer_address: "A1".into(), token_address: "T1".into(), amount: 800, refunded_amount: 0, status: "PartiallyRefunded".into(), paid_at: 3000 },
+        ]
+    }
+
+    struct StaticPayments(Vec<PaymentRecord>);
+    struct StaticMerchants(Vec<MerchantRecord>);
+    struct StaticRefunds(Vec<RefundRecord>);
+    impl PaymentIndex for StaticPayments { fn all(&self) -> Vec<PaymentRecord> { self.0.clone() } }
+    impl MerchantIndex for StaticMerchants { fn all(&self) -> Vec<MerchantRecord> { self.0.clone() } }
+    impl RefundIndex for StaticRefunds { fn all(&self) -> Vec<RefundRecord> { self.0.clone() } }
+
+    fn svc() -> SearchService<StaticPayments, StaticMerchants, StaticRefunds> {
+        SearchService::new(
+            StaticPayments(payments()),
+            StaticMerchants(vec![
+                MerchantRecord { address: "M1".into(), name: "Coffee House".into(), category: "Food".into(), active: true, whitelisted: false, registered_at: 100 },
+                MerchantRecord { address: "M2".into(), name: "Tech Store".into(), category: "Digital".into(), active: false, whitelisted: true, registered_at: 200 },
+            ]),
+            StaticRefunds(vec![
+                RefundRecord { refund_id: "R1".into(), order_id: "P1".into(), amount: 100, status: "Pending".into(), initiated_by: "A1".into(), initiated_at: 1500 },
+            ]),
+        )
+    }
+
+    #[test] fn filter_by_merchant() {
+        let page = svc().search_payments(PaymentSearchQuery { merchant_address: Some("M1".into()), ..Default::default() });
+        assert_eq!(page.records.len(), 2);
+    }
+
+    #[test] fn filter_by_amount_range() {
+        let page = svc().search_payments(PaymentSearchQuery { amount_min: Some(300), amount_max: Some(600), ..Default::default() });
+        assert_eq!(page.records.len(), 1);
+        assert_eq!(page.records[0].order_id, "P1");
+    }
+
+    #[test] fn filter_by_date_range() {
+        let page = svc().search_payments(PaymentSearchQuery { date_start: Some(1500), date_end: Some(2500), ..Default::default() });
+        assert_eq!(page.records.len(), 1);
+        assert_eq!(page.records[0].order_id, "P2");
+    }
+
+    #[test] fn sort_by_amount_ascending() {
+        let page = svc().search_payments(PaymentSearchQuery { sort_field: Some(PaymentSortField::Amount), sort_order: Some(SortOrder::Ascending), ..Default::default() });
+        assert_eq!(page.records[0].amount, 200);
+    }
+
+    #[test] fn cursor_pagination() {
+        let page1 = svc().search_payments(PaymentSearchQuery { limit: Some(2), sort_field: Some(PaymentSortField::Date), sort_order: Some(SortOrder::Descending), ..Default::default() });
+        assert_eq!(page1.records.len(), 2);
+        assert!(page1.next_cursor.is_some());
+        let page2 = svc().search_payments(PaymentSearchQuery { limit: Some(2), cursor: page1.next_cursor, sort_field: Some(PaymentSortField::Date), sort_order: Some(SortOrder::Descending), ..Default::default() });
+        assert_eq!(page2.records.len(), 1);
+        assert!(page2.next_cursor.is_none());
+    }
+
+    #[test] fn merchant_text_search() {
+        let page = svc().search_merchants(MerchantSearchQuery { name_contains: Some("coffee".into()), ..Default::default() });
+        assert_eq!(page.records.len(), 1);
+    }
+
+    #[test] fn merchant_filter_active() {
+        let page = svc().search_merchants(MerchantSearchQuery { active: Some(false), ..Default::default() });
+        assert_eq!(page.records.len(), 1);
+        assert_eq!(page.records[0].address, "M2");
+    }
+
+    #[test] fn refund_filter_by_order() {
+        let page = svc().search_refunds(RefundSearchQuery { order_id: Some("P1".into()), ..Default::default() });
+        assert_eq!(page.records.len(), 1);
+    }
+}
diff --git a/services/search/types.rs b/services/search/types.rs
new file mode 100644
index 0000000..222cafb
--- /dev/null
+++ b/services/search/types.rs
@@ -0,0 +1,153 @@
+/// Advanced search & filtering types — Issue #275
+
+use serde::{Deserialize, Serialize};
+
+// ── Sort helpers ──────────────────────────────────────────────────────────────
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum SortOrder {
+    Ascending,
+    Descending,
+}
+
+// ── Payment search ────────────────────────────────────────────────────────────
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum PaymentSortField {
+    Date,
+    Amount,
+    MerchantAddress,
+    PayerAddress,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum PaymentStatusFilter {
+    Any,
+    Completed,
+    PartiallyRefunded,
+    FullyRefunded,
+}
+
+#[derive(Debug, Clone, Default, Deserialize)]
+pub struct PaymentSearchQuery {
+    // text
+    pub merchant_address: Option<String>,
+    pub payer_address: Option<String>,
+    pub token_address: Option<String>,
+    // amount range
+    pub amount_min: Option<i128>,
+    pub amount_max: Option<i128>,
+    // date range
+    pub date_start: Option<u64>,
+    pub date_end: Option<u64>,
+    // status (supports multiple values)
+    pub statuses: Option<Vec<PaymentStatusFilter>>,
+    // sort
+    pub sort_field: Option<PaymentSortField>,
+    pub sort_order: Option<SortOrder>,
+    // pagination
+    pub cursor: Option<String>,
+    pub limit: Option<u32>,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct PaymentRecord {
+    pub order_id: String,
+    pub merchant_address: String,
+    pub payer_address: String,
+    pub token_address: String,
+    pub amount: i128,
+    pub refunded_amount: i128,
+    pub status: String,
+    pub paid_at: u64,
+}
+
+#[derive(Debug, Serialize)]
+pub struct PaymentPage {
+    pub records: Vec<PaymentRecord>,
+    pub next_cursor: Option<String>,
+    pub total: u64,
+}
+
+// ── Merchant search ───────────────────────────────────────────────────────────
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum MerchantSortField {
+    Name,
+    RegisteredAt,
+    Category,
+}
+
+#[derive(Debug, Clone, Default, Deserialize)]
+pub struct MerchantSearchQuery {
+    pub name_contains: Option<String>,
+    pub category: Option<String>,
+    pub active: Option<bool>,
+    pub whitelisted: Option<bool>,
+    pub sort_field: Option<MerchantSortField>,
+    pub sort_order: Option<SortOrder>,
+    pub cursor: Option<String>,
+    pub limit: Option<u32>,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct MerchantRecord {
+    pub address: String,
+    pub name: String,
+    pub category: String,
+    pub active: bool,
+    pub whitelisted: bool,
+    pub registered_at: u64,
+}
+
+#[derive(Debug, Serialize)]
+pub struct MerchantPage {
+    pub records: Vec<MerchantRecord>,
+    pub next_cursor: Option<String>,
+    pub total: u64,
+}
+
+// ── Refund search ─────────────────────────────────────────────────────────────
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum RefundSortField {
+    InitiatedAt,
+    Amount,
+}
+
+#[derive(Debug, Clone, Default, Deserialize)]
+pub struct RefundSearchQuery {
+    pub order_id: Option<String>,
+    pub initiated_by: Option<String>,
+    pub statuses: Option<Vec<String>>,
+    pub date_start: Option<u64>,
+    pub date_end: Option<u64>,
+    pub amount_min: Option<i128>,
+    pub amount_max: Option<i128>,
+    pub sort_field: Option<RefundSortField>,
+    pub sort_order: Option<SortOrder>,
+    pub cursor: Option<String>,
+    pub limit: Option<u32>,
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct RefundRecord {
+    pub refund_id: String,
+    pub order_id: String,
+    pub amount: i128,
+    pub status: String,
+    pub initiated_by: String,
+    pub initiated_at: u64,
+}
+
+#[derive(Debug, Serialize)]
+pub struct RefundPage {
+    pub records: Vec<RefundRecord>,
+    pub next_cursor: Option<String>,
+    pub total: u64,
+}