diff --git a/src/parse-selector.test.ts b/src/parse-selector.test.ts
index 39d15e3..b55fe83 100644
--- a/src/parse-selector.test.ts
+++ b/src/parse-selector.test.ts
@@ -1739,4 +1739,241 @@ describe('parse_selector()', () => {
 		expect(result.has_children).toBe(true)
 		expect(result.children.length).toBeGreaterThan(0)
 	})
+
+	describe('Namespace selectors', () => {
+		test('should parse ns|* (namespace with universal selector)', () => {
+			const result = parse_selector('ns|*')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('ns|*')
+
+			const selector = result.first_child
+			expect(selector?.type).toBe(NODE_SELECTOR)
+			expect(selector?.text).toBe('ns|*')
+
+			const universal = selector?.first_child
+			expect(universal?.type).toBe(NODE_SELECTOR_UNIVERSAL)
+			expect(universal?.text).toBe('ns|*')
+			expect(universal?.name).toBe('ns')
+		})
+
+		test('should parse ns|div (namespace with type selector)', () => {
+			const result = parse_selector('ns|div')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('ns|div')
+
+			const selector = result.first_child
+			expect(selector?.type).toBe(NODE_SELECTOR)
+
+			const typeSelector = selector?.first_child
+			expect(typeSelector?.type).toBe(NODE_SELECTOR_TYPE)
+			expect(typeSelector?.text).toBe('ns|div')
+			expect(typeSelector?.name).toBe('ns')
+		})
+
+		test('should parse *|* (any namespace with universal selector)', () => {
+			const result = parse_selector('*|*')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('*|*')
+
+			const selector = result.first_child
+			const universal = selector?.first_child
+			expect(universal?.type).toBe(NODE_SELECTOR_UNIVERSAL)
+			expect(universal?.text).toBe('*|*')
+			expect(universal?.name).toBe('*')
+		})
+
+		test('should parse *|div (any namespace with type selector)', () => {
+			const result = parse_selector('*|div')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('*|div')
+
+			const selector = result.first_child
+			const typeSelector = selector?.first_child
+			expect(typeSelector?.type).toBe(NODE_SELECTOR_TYPE)
+			expect(typeSelector?.text).toBe('*|div')
+			expect(typeSelector?.name).toBe('*')
+		})
+
+		test('should parse |* (empty namespace with universal selector)', () => {
+			const result = parse_selector('|*')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('|*')
+
+			const selector = result.first_child
+			const universal = selector?.first_child
+			expect(universal?.type).toBe(NODE_SELECTOR_UNIVERSAL)
+			expect(universal?.text).toBe('|*')
+			// Empty namespace should result in empty name
+			expect(universal?.name).toBe('|')
+		})
+
+		test('should parse |div (empty namespace with type selector)', () => {
+			const result = parse_selector('|div')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('|div')
+
+			const selector = result.first_child
+			const typeSelector = selector?.first_child
+			expect(typeSelector?.type).toBe(NODE_SELECTOR_TYPE)
+			expect(typeSelector?.text).toBe('|div')
+			// Empty namespace should result in empty name
+			expect(typeSelector?.name).toBe('|')
+		})
+
+		test('should parse namespace selector with class', () => {
+			const result = parse_selector('ns|div.class')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('ns|div.class')
+
+			const selector = result.first_child
+			const children = selector?.children || []
+			expect(children.length).toBe(2)
+			expect(children[0].type).toBe(NODE_SELECTOR_TYPE)
+			expect(children[0].text).toBe('ns|div')
+			expect(children[0].name).toBe('ns')
+			expect(children[1].type).toBe(NODE_SELECTOR_CLASS)
+		})
+
+		test('should parse namespace selector with ID', () => {
+			const result = parse_selector('ns|*#id')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('ns|*#id')
+
+			const selector = result.first_child
+			const children = selector?.children || []
+			expect(children.length).toBe(2)
+			expect(children[0].type).toBe(NODE_SELECTOR_UNIVERSAL)
+			expect(children[0].text).toBe('ns|*')
+			expect(children[1].type).toBe(NODE_SELECTOR_ID)
+		})
+
+		test('should parse namespace selector in complex selector', () => {
+			const result = parse_selector('ns|div > *|span')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('ns|div > *|span')
+
+			const selector = result.first_child
+			const children = selector?.children || []
+			expect(children.length).toBe(3) // div, >, span
+			expect(children[0].type).toBe(NODE_SELECTOR_TYPE)
+			expect(children[0].text).toBe('ns|div')
+			expect(children[1].type).toBe(NODE_SELECTOR_COMBINATOR)
+			expect(children[2].type).toBe(NODE_SELECTOR_TYPE)
+			expect(children[2].text).toBe('*|span')
+		})
+
+		test('should parse namespace selector in selector list', () => {
+			const result = parse_selector('ns|div, |span, *|p')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('ns|div, |span, *|p')
+
+			const selectors = result.children
+			expect(selectors.length).toBe(3)
+
+			const firstType = selectors[0].first_child
+			expect(firstType?.type).toBe(NODE_SELECTOR_TYPE)
+			expect(firstType?.text).toBe('ns|div')
+			expect(firstType?.name).toBe('ns')
+
+			const secondType = selectors[1].first_child
+			expect(secondType?.type).toBe(NODE_SELECTOR_TYPE)
+			expect(secondType?.text).toBe('|span')
+			expect(secondType?.name).toBe('|')
+
+			const thirdType = selectors[2].first_child
+			expect(thirdType?.type).toBe(NODE_SELECTOR_TYPE)
+			expect(thirdType?.text).toBe('*|p')
+			expect(thirdType?.name).toBe('*')
+		})
+
+		test('should parse namespace selector with attribute', () => {
+			const result = parse_selector('ns|div[attr="value"]')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('ns|div[attr="value"]')
+
+			const selector = result.first_child
+			const children = selector?.children || []
+			expect(children.length).toBe(2)
+			expect(children[0].type).toBe(NODE_SELECTOR_TYPE)
+			expect(children[0].name).toBe('ns')
+			expect(children[1].type).toBe(NODE_SELECTOR_ATTRIBUTE)
+		})
+
+		test('should parse namespace selector with pseudo-class', () => {
+			const result = parse_selector('ns|a:hover')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('ns|a:hover')
+
+			const selector = result.first_child
+			const children = selector?.children || []
+			expect(children.length).toBe(2)
+			expect(children[0].type).toBe(NODE_SELECTOR_TYPE)
+			expect(children[0].name).toBe('ns')
+			expect(children[1].type).toBe(NODE_SELECTOR_PSEUDO_CLASS)
+		})
+
+		test('should parse namespace with various identifiers', () => {
+			const result = parse_selector('svg|rect')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('svg|rect')
+
+			const selector = result.first_child
+			const typeSelector = selector?.first_child
+			expect(typeSelector?.type).toBe(NODE_SELECTOR_TYPE)
+			expect(typeSelector?.text).toBe('svg|rect')
+			expect(typeSelector?.name).toBe('svg')
+		})
+
+		test('should parse long namespace identifier', () => {
+			const result = parse_selector('myNamespace|element')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe('myNamespace|element')
+
+			const selector = result.first_child
+			const typeSelector = selector?.first_child
+			expect(typeSelector?.type).toBe(NODE_SELECTOR_TYPE)
+			expect(typeSelector?.name).toBe('myNamespace')
+		})
+
+		test('should handle namespace in nested pseudo-class', () => {
+			const result = parse_selector(':is(ns|div, *|span)')
+
+			expect(result.type).toBe(NODE_SELECTOR_LIST)
+			expect(result.text).toBe(':is(ns|div, *|span)')
+
+			const selector = result.first_child
+			const pseudo = selector?.first_child
+			expect(pseudo?.type).toBe(NODE_SELECTOR_PSEUDO_CLASS)
+			expect(pseudo?.name).toBe('is')
+
+			// The content should contain namespace selectors
+			const nestedList = pseudo?.first_child
+			expect(nestedList?.type).toBe(NODE_SELECTOR_LIST)
+
+			const nestedSelectors = nestedList?.children || []
+			expect(nestedSelectors.length).toBe(2)
+
+			const firstNestedType = nestedSelectors[0].first_child
+			expect(firstNestedType?.type).toBe(NODE_SELECTOR_TYPE)
+			expect(firstNestedType?.text).toBe('ns|div')
+
+			const secondNestedType = nestedSelectors[1].first_child
+			expect(secondNestedType?.type).toBe(NODE_SELECTOR_TYPE)
+			expect(secondNestedType?.text).toBe('*|span')
+		})
+	})
 })
diff --git a/src/parse-selector.ts b/src/parse-selector.ts
index f6d88fe..26a0eff 100644
--- a/src/parse-selector.ts
+++ b/src/parse-selector.ts
@@ -296,25 +296,29 @@ export class SelectorParser {
 
 		switch (token_type) {
 			case TOKEN_IDENT:
-				// Type selector: div, span, p
-				return this.create_node(NODE_SELECTOR_TYPE, start, end)
+				// Could be a type selector or namespace prefix
+				// Check if followed by | (namespace separator)
+				return this.parse_type_or_namespace_selector(start, end)
 
 			case TOKEN_HASH:
 				// ID selector: #id
 				return this.create_node(NODE_SELECTOR_ID, start, end)
 
 			case TOKEN_DELIM:
-				// Could be: . (class), * (universal), & (nesting)
+				// Could be: . (class), * (universal), & (nesting), | (namespace)
 				let ch = this.source.charCodeAt(start)
 				if (ch === CHAR_PERIOD) {
 					// . - class selector
 					return this.parse_class_selector(start)
 				} else if (ch === CHAR_ASTERISK) {
-					// * - universal selector
-					return this.create_node(NODE_SELECTOR_UNIVERSAL, start, end)
+					// * - could be universal selector or namespace prefix (*|)
+					return this.parse_universal_or_namespace_selector(start, end)
 				} else if (ch === CHAR_AMPERSAND) {
 					// & - nesting selector
 					return this.create_node(NODE_SELECTOR_NESTING, start, end)
+				} else if (ch === CHAR_PIPE) {
+					// | - empty namespace prefix (|E or |*)
+					return this.parse_empty_namespace_selector(start)
 				}
 				// Other delimiters signal end of selector
 				return null
@@ -341,6 +345,78 @@ export class SelectorParser {
 		}
 	}
 
+	// Parse the local part after | in a namespace selector (E or *)
+	// Returns the node type (TYPE or UNIVERSAL) or null if invalid
+	private parse_namespace_local_part(
+		selector_start: number,
+		namespace_start: number,
+		namespace_length: number,
+	): number | null {
+		const saved = this.lexer.save_position()
+		this.lexer.next_token_fast(false)
+
+		let node_type: number
+		if (this.lexer.token_type === TOKEN_IDENT) {
+			// ns|type
+			node_type = NODE_SELECTOR_TYPE
+		} else if (
+			this.lexer.token_type === TOKEN_DELIM &&
+			this.source.charCodeAt(this.lexer.token_start) === CHAR_ASTERISK
+		) {
+			// ns|*
+			node_type = NODE_SELECTOR_UNIVERSAL
+		} else {
+			// Invalid - restore position
+			this.lexer.restore_position(saved)
+			return null
+		}
+
+		let node = this.create_node(node_type, selector_start, this.lexer.token_end)
+		// Store namespace in content fields
+		this.arena.set_content_start(node, namespace_start)
+		this.arena.set_content_length(node, namespace_length)
+		return node
+	}
+
+	// Parse type selector or namespace selector (ns|E or ns|*)
+	// Called when we've seen an IDENT token
+	private parse_type_or_namespace_selector(start: number, end: number): number | null {
+		// Check if followed by | (namespace separator)
+		if (this.lexer.pos < this.selector_end && this.source.charCodeAt(this.lexer.pos) === CHAR_PIPE) {
+			this.lexer.pos++ // skip |
+			let node = this.parse_namespace_local_part(start, start, end - start)
+			if (node !== null) return node
+			// Invalid - restore and treat as regular type selector
+			this.lexer.pos = end
+		}
+
+		// Regular type selector (no namespace)
+		return this.create_node(NODE_SELECTOR_TYPE, start, end)
+	}
+
+	// Parse universal selector or namespace selector (*|E or *|*)
+	// Called when we've seen a * DELIM token
+	private parse_universal_or_namespace_selector(start: number, end: number): number | null {
+		// Check if followed by | (any-namespace prefix)
+		if (this.lexer.pos < this.selector_end && this.source.charCodeAt(this.lexer.pos) === CHAR_PIPE) {
+			this.lexer.pos++ // skip |
+			let node = this.parse_namespace_local_part(start, start, end - start)
+			if (node !== null) return node
+			// Invalid - restore and treat as regular universal selector
+			this.lexer.pos = end
+		}
+
+		// Regular universal selector (no namespace)
+		return this.create_node(NODE_SELECTOR_UNIVERSAL, start, end)
+	}
+
+	// Parse empty namespace selector (|E or |*)
+	// Called when we've seen a | DELIM token at the start
+	private parse_empty_namespace_selector(start: number): number | null {
+		// The | character is the namespace indicator (length = 1)
+		return this.parse_namespace_local_part(start, start, 1)
+	}
+
 	// Parse combinator (>, +, ~, or descendant space)
 	private try_parse_combinator(): number | null {
 		let whitespace_start = this.lexer.pos