diff --git a/bun.lockb b/bun.lockb
index 3134477..9692b5c 100755
Binary files a/bun.lockb and b/bun.lockb differ
diff --git a/filter.test.ts b/filter.test.ts
index eb07079..22ec0b7 100644
--- a/filter.test.ts
+++ b/filter.test.ts
@@ -237,4 +237,247 @@ describe('Filter', () => {
       expect(getFilterLimit({ '#p': [] })).toEqual(0)
     })
   })
+
+  describe('NIP-91 AND filters', () => {
+    describe('matchFilter', () => {
+      test('should return true when all AND filter values are present', () => {
+        const filter = { '&t': ['meme', 'cat'] }
+        const event = buildEvent({
+          tags: [
+            ['t', 'meme'],
+            ['t', 'cat'],
+          ],
+        })
+        const result = matchFilter(filter, event)
+        expect(result).toEqual(true)
+      })
+
+      test('should return false when one AND filter value is missing', () => {
+        const filter = { '&t': ['meme', 'cat'] }
+        const event = buildEvent({
+          tags: [['t', 'meme']],
+        })
+        const result = matchFilter(filter, event)
+        expect(result).toEqual(false)
+      })
+
+      test('should return false when all AND filter values are missing', () => {
+        const filter = { '&t': ['meme', 'cat'] }
+        const event = buildEvent({
+          tags: [['t', 'dog']],
+        })
+        const result = matchFilter(filter, event)
+        expect(result).toEqual(false)
+      })
+
+      test('should return true when AND filter has single value that matches', () => {
+        const filter = { '&t': ['meme'] }
+        const event = buildEvent({
+          tags: [['t', 'meme']],
+        })
+        const result = matchFilter(filter, event)
+        expect(result).toEqual(true)
+      })
+
+      test('should handle multiple AND filters', () => {
+        const filter = {
+          '&t': ['meme', 'cat'],
+          '&p': ['pubkey1', 'pubkey2'],
+        }
+        const event = buildEvent({
+          tags: [
+            ['t', 'meme'],
+            ['t', 'cat'],
+            ['p', 'pubkey1'],
+            ['p', 'pubkey2'],
+          ],
+        })
+        const result = matchFilter(filter, event)
+        expect(result).toEqual(true)
+      })
+
+      test('should return false when one of multiple AND filters fails', () => {
+        const filter = {
+          '&t': ['meme', 'cat'],
+          '&p': ['pubkey1', 'pubkey2'],
+        }
+        const event = buildEvent({
+          tags: [
+            ['t', 'meme'],
+            ['t', 'cat'],
+            ['p', 'pubkey1'],
+          ],
+        })
+        const result = matchFilter(filter, event)
+        expect(result).toEqual(false)
+      })
+
+      test('NIP-91 example: AND takes precedence, OR excludes AND values', () => {
+        const filter = {
+          kinds: [1],
+          '&t': ['meme', 'cat'],
+          '#t': ['black', 'white'],
+        }
+        // Event with both AND values and one OR value
+        const event1 = buildEvent({
+          kind: 1,
+          tags: [
+            ['t', 'meme'],
+            ['t', 'cat'],
+            ['t', 'black'],
+          ],
+        })
+        expect(matchFilter(filter, event1)).toEqual(true)
+
+        // Event with both AND values and other OR value
+        const event2 = buildEvent({
+          kind: 1,
+          tags: [
+            ['t', 'meme'],
+            ['t', 'cat'],
+            ['t', 'white'],
+          ],
+        })
+        expect(matchFilter(filter, event2)).toEqual(true)
+
+        // Event with both AND values but no OR values
+        const event3 = buildEvent({
+          kind: 1,
+          tags: [
+            ['t', 'meme'],
+            ['t', 'cat'],
+          ],
+        })
+        expect(matchFilter(filter, event3)).toEqual(false)
+
+        // Event missing one AND value
+        const event4 = buildEvent({
+          kind: 1,
+          tags: [
+            ['t', 'meme'],
+            ['t', 'black'],
+          ],
+        })
+        expect(matchFilter(filter, event4)).toEqual(false)
+
+        // Event with AND values that are also in OR (should be excluded from OR check)
+        const event5 = buildEvent({
+          kind: 1,
+          tags: [
+            ['t', 'meme'],
+            ['t', 'cat'],
+            ['t', 'meme'], // duplicate, but AND values should be excluded from OR
+          ],
+        })
+        expect(matchFilter(filter, event5)).toEqual(false) // No OR values remain after exclusion
+      })
+
+      test('should exclude AND values from OR filter matching', () => {
+        const filter = {
+          '&t': ['meme'],
+          '#t': ['meme', 'cat'],
+        }
+        // Event has 'meme' (in AND) and 'cat' (in OR, not in AND)
+        const event1 = buildEvent({
+          tags: [
+            ['t', 'meme'],
+            ['t', 'cat'],
+          ],
+        })
+        expect(matchFilter(filter, event1)).toEqual(true)
+
+        // Event has only 'meme' (in AND, excluded from OR)
+        const event2 = buildEvent({
+          tags: [['t', 'meme']],
+        })
+        expect(matchFilter(filter, event2)).toEqual(false) // No OR values remain
+      })
+
+      test('should handle AND filter with empty array', () => {
+        const filter = { '&t': [] }
+        const event = buildEvent({
+          tags: [['t', 'meme']],
+        })
+        // Empty AND filter should pass (no requirements)
+        const result = matchFilter(filter, event)
+        expect(result).toEqual(true)
+      })
+
+      test('should work with other filter conditions', () => {
+        const filter = {
+          kinds: [1],
+          authors: ['abc'],
+          '&t': ['meme', 'cat'],
+        }
+        const event = buildEvent({
+          kind: 1,
+          pubkey: 'abc',
+          tags: [
+            ['t', 'meme'],
+            ['t', 'cat'],
+          ],
+        })
+        const result = matchFilter(filter, event)
+        expect(result).toEqual(true)
+      })
+
+      test('should work with OR filter only (backward compatibility)', () => {
+        const filter = { '#t': ['meme', 'cat'] }
+        const event = buildEvent({
+          tags: [['t', 'meme']],
+        })
+        const result = matchFilter(filter, event)
+        expect(result).toEqual(true)
+      })
+    })
+
+    describe('mergeFilters', () => {
+      test('should merge AND filters', () => {
+        const result = mergeFilters({ '&t': ['meme'] }, { '&t': ['cat'] })
+        expect(result).toEqual({
+          '&t': ['meme', 'cat'],
+        })
+      })
+
+      test('should merge AND and OR filters separately', () => {
+        const result = mergeFilters({ '&t': ['meme'], '#t': ['black'] }, { '&t': ['cat'], '#t': ['white'] })
+        expect(result).toEqual({
+          '&t': ['meme', 'cat'],
+          '#t': ['black', 'white'],
+        })
+      })
+
+      test('should merge mixed filters with AND filters', () => {
+        const result = mergeFilters({ kinds: [1], '&t': ['meme'], limit: 3 }, { kinds: [2], '&t': ['cat'], limit: 5 })
+        expect(result).toEqual({
+          kinds: [1, 2],
+          '&t': ['meme', 'cat'],
+          limit: 5,
+        })
+      })
+
+      test('should deduplicate AND filter values', () => {
+        const result = mergeFilters({ '&t': ['meme', 'cat'] }, { '&t': ['meme', 'dog'] })
+        expect(result).toEqual({
+          '&t': ['meme', 'cat', 'dog'],
+        })
+      })
+    })
+
+    describe('getFilterLimit', () => {
+      test('empty AND filters return 0', () => {
+        expect(getFilterLimit({ '&t': [] })).toEqual(0)
+      })
+
+      test('should handle AND filters with other conditions', () => {
+        expect(getFilterLimit({ '&t': ['meme', 'cat'] })).toEqual(Infinity)
+        expect(getFilterLimit({ ids: ['123'], '&t': ['meme'] })).toEqual(1)
+      })
+
+      test('should handle both AND and OR filters', () => {
+        expect(getFilterLimit({ '&t': ['meme'], '#p': ['pubkey1'] })).toEqual(Infinity)
+        expect(getFilterLimit({ '&t': [], '#p': [] })).toEqual(0)
+      })
+    })
+  })
 })
diff --git a/filter.ts b/filter.ts
index a469b31..0a8fea4 100644
--- a/filter.ts
+++ b/filter.ts
@@ -10,6 +10,7 @@ export type Filter = {
   limit?: number
   search?: string
   [key: `#${string}`]: string[] | undefined
+  [key: `&${string}`]: string[] | undefined
 }
 
 export function matchFilter(filter: Filter, event: Event): boolean {
@@ -23,11 +24,43 @@ export function matchFilter(filter: Filter, event: Event): boolean {
     return false
   }
 
+  // Track AND filter values to exclude from OR filters
+  const andFilterValues: Map<string, Set<string>> = new Map()
+
+  // Process AND filters first (they take precedence)
+  for (let f in filter) {
+    if (f[0] === '&') {
+      let tagName = f.slice(1)
+      let values = filter[`&${tagName}` as `&${string}`]
+      if (values) {
+        // Check that ALL values in the AND filter are present in the event's tags
+        const eventTagValues = new Set(event.tags.filter(([t]) => t === tagName).map(([, v]) => v))
+        for (let i = 0; i < values.length; i++) {
+          if (!eventTagValues.has(values[i])) return false
+        }
+
+        // Store AND filter values to exclude from OR filters
+        andFilterValues.set(tagName, new Set(values))
+      }
+    }
+  }
+
+  // Process OR filters (excluding values that appear in AND filters)
   for (let f in filter) {
     if (f[0] === '#') {
       let tagName = f.slice(1)
       let values = filter[`#${tagName}`]
-      if (values && !event.tags.find(([t, v]) => t === f.slice(1) && values!.indexOf(v) !== -1)) return false
+      if (values) {
+        // Exclude values that are in the corresponding AND filter
+        const andValues = andFilterValues.get(tagName)
+        const orValues = andValues ? values.filter(v => !andValues.has(v)) : values
+
+        // If all OR values were excluded, the OR filter cannot be satisfied
+        if (orValues.length === 0) return false
+
+        // Check if any of the remaining OR values match
+        if (!event.tags.find(([t, v]) => t === tagName && orValues.indexOf(v) !== -1)) return false
+      }
     }
   }
 
@@ -51,7 +84,13 @@ export function mergeFilters(...filters: Filter[]): Filter {
   for (let i = 0; i < filters.length; i++) {
     let filter = filters[i]
     Object.entries(filter).forEach(([property, values]) => {
-      if (property === 'kinds' || property === 'ids' || property === 'authors' || property[0] === '#') {
+      if (
+        property === 'kinds' ||
+        property === 'ids' ||
+        property === 'authors' ||
+        property[0] === '#' ||
+        property[0] === '&'
+      ) {
         // @ts-ignore
         result[property] = result[property] || []
         // @ts-ignore
@@ -82,7 +121,7 @@ export function getFilterLimit(filter: Filter): number {
   if (filter.authors && !filter.authors.length) return 0
 
   for (const [key, value] of Object.entries(filter)) {
-    if (key[0] === '#' && Array.isArray(value) && !value.length) return 0
+    if ((key[0] === '#' || key[0] === '&') && Array.isArray(value) && !value.length) return 0
   }
 
   return Math.min(