diff --git a/LANGUAGE.md b/LANGUAGE.md
index 2ea40ef..86d8956 100644
--- a/LANGUAGE.md
+++ b/LANGUAGE.md
@@ -30,6 +30,7 @@ roadmap and milestone history.
 - exact-width integers, concrete pointer-sized `isize` / `usize`, `f32`, `f64`, `bool`, `void`, `noreturn`, and `anyopaque`; `noreturn` is a bottom type valid as a native function result and coerces to any expected value type; contextual `int` accepts the whole integer family, while `uint` accepts only unsigned native and target-classified C integers
 - target-dependent C scalar primitives from `c_char` through `c_longdouble`, kept semantically distinct from native scalars
 - contextual integer/float/character literals, backward type-demand inference through names and arithmetic/bitwise expressions, and typed compile-time evaluation for numeric constant expressions
+- integer literals use decimal digits or explicit binary `0b`, octal `0o`, and hexadecimal `0x` prefixes; uppercase prefixes and hexadecimal digits are also accepted. leading-zero unprefixed literals remain decimal, signs remain unary operators, and tuple ordinals remain canonical decimal. digits must match the base and magnitudes must fit `u64` before contextual range checking; digit separators and nondecimal floating-point literals are not supported.
 - strict numeric conversion by default, widening where valid, C scalar coercions at C boundaries, and explicit scalar casts through keywords or transparent aliases, such as `i32(x)`, `c_float(x)`, or `StringId(x)`
 - implicit contextual integer constants must be exactly representable in the destination float, including folded expressions and inferred constants; `f32` rejects `16777217` but accepts `16777218`, while `f64` rejects `9007199254740993` but accepts `9007199254740994`; powers of two remain exact
 - float literals retain IEEE rounding, and explicit scalar casts such as `f32(16777217)` or `f64(9007199254740993)` deliberately permit rounding; existing typed-value widening and C scalar coercion rules are unchanged
diff --git a/README.md b/README.md
index d9d00ba..972b975 100644
--- a/README.md
+++ b/README.md
@@ -248,6 +248,7 @@ Current prototype features:
 - String literals as immutable pointers to static zero-terminated byte arrays
 - Pointer-preserving `.ptr`/`.len`, pointer-to-array indexing and slicing, postfix pointer dereference and optional unwrap, and keyed struct literals
 - Contextual integer constants and typed compile-time evaluation of arithmetic and Zig-style bitwise expressions
+- Decimal, binary (`0b101010`), octal (`0o52`), and hexadecimal (`0x2a`) integer literals, with uppercase prefix variants, checked `u64` magnitudes, and ordinary contextual typing; leading zeros alone do not select octal
 - Contextual integer-to-float constants require exact representation (`f32` accepts `16777218`, not `16777217`; `f64` accepts `9007199254740994`, not `9007199254740993`), including folded and inferred constants; float literals and explicit scalar casts retain IEEE rounding
 - Integer `~`, `&`, `|`, `xor`, guarded `<<` / `>>`, saturating `<<|`, and their compound assignments; postfix `^` remains pointer dereference
 - Scalar-backed nominal `distinct` types with same-identity runtime/comptime operators, explicit backing extraction casts, integer bounds, reflection, and recursive standard formatting
diff --git a/compiler/lexer/lexer.odin b/compiler/lexer/lexer.odin
index 463c4c0..720f47f 100644
--- a/compiler/lexer/lexer.odin
+++ b/compiler/lexer/lexer.odin
@@ -411,6 +411,35 @@ lex :: proc(
 		case:
 			if value >= '0' && value <= '9' {
 				start := cursor
+				base: byte
+				if value == '0' && cursor+1 < len(bytes) {
+					switch bytes[cursor+1] {
+					case 'b', 'B': base = 2
+					case 'o', 'O': base = 8
+					case 'x', 'X': base = 16
+					}
+				}
+				if base != 0 {
+					cursor += 2
+					digits_start := cursor
+					valid := true
+					for cursor < len(bytes) && is_identifier_continue(bytes[cursor]) {
+						digit := bytes[cursor]
+						valid = valid && is_hex_digit(digit) && (base == 16 || digit-'0' < base)
+						cursor += 1
+					}
+					if !valid || cursor == digits_start {
+						id := source.add(
+							diagnostics,
+							source.Span{file=source_file.id, start=source.Offset(start), end=source.Offset(cursor)},
+							"invalid digits in prefixed integer literal",
+						)
+						append_token(&stream, source_file, .Invalid, start, cursor, diagnostic=id)
+					} else {
+						append_token(&stream, source_file, .Integer, start, cursor)
+					}
+					continue
+				}
 				for cursor < len(bytes) && bytes[cursor] >= '0' && bytes[cursor] <= '9' {
 					cursor += 1
 				}
diff --git a/compiler/parser/parser.odin b/compiler/parser/parser.odin
index decf0ee..a2152bc 100644
--- a/compiler/parser/parser.odin
+++ b/compiler/parser/parser.odin
@@ -239,6 +239,7 @@ parse_type_constant :: proc(parser: ^Parser) -> (u64, bool) {
 		advance(parser)
 		value, ok := parse_integer_magnitude(token_text(parser, tok))
 		if !ok {
+			source.add(parser.diagnostics, tok.span, "integer literal magnitude does not fit in u64")
 			return 0, false
 		}
 		if negative {
@@ -906,21 +907,37 @@ parse_anonymous_struct_type_expr :: proc(parser: ^Parser) -> ast.Expr_Id {
 }
 
 parse_integer_magnitude :: proc(text: string) -> (u64, bool) {
+	base := u64(10)
+	digits := text
+	if len(text) >= 2 && text[0] == '0' {
+		switch text[1] {
+		case 'b', 'B': base = 2
+		case 'o', 'O': base = 8
+		case 'x', 'X': base = 16
+		}
+		if base != 10 {
+			digits = text[2:]
+		}
+	}
 	value: u64
-	for byte in transmute([]byte)text {
-		if byte < '0' || byte > '9' {
+	for byte in transmute([]byte)digits {
+		if !(byte >= '0' && byte <= '9' || byte >= 'a' && byte <= 'f' || byte >= 'A' && byte <= 'F') {
 			return 0, false
 		}
-		next, overflow := intrinsics.overflow_mul(value, u64(10))
+		digit := u64(decode_hex_digit(byte))
+		if digit >= base {
+			return 0, false
+		}
+		next, overflow := intrinsics.overflow_mul(value, base)
 		if overflow {
 			return 0, false
 		}
-		value, overflow = intrinsics.overflow_add(next, u64(byte-'0'))
+		value, overflow = intrinsics.overflow_add(next, digit)
 		if overflow {
 			return 0, false
 		}
 	}
-	return value, len(text) > 0
+	return value, len(digits) > 0
 }
 
 parse_primary :: proc(parser: ^Parser, nesting: int) -> ast.Expr_Id {
diff --git a/compiler_tests.odin b/compiler_tests.odin
index 6540e38..3ae3951 100644
--- a/compiler_tests.odin
+++ b/compiler_tests.odin
@@ -86,6 +86,137 @@ main func() void { _ = value }
 	testing.expect_value(t, module.statements[module.functions[0].body[0]].name, sink_symbol)
 }
 
+@(test)
+integer_base_literals_compile_and_run :: proc(t: ^testing.T) {
+	directory := "/tmp/brolang-test-integer-bases"
+	output := "/tmp/brolang-test-integer-bases-output"
+	text := `Flags :: enum(u8) { one = 0b0001, two = 0o2, four = 0x04 }
+maximum u64 :: 0xffffffffffffffff
+minimum i64 :: -0x8000000000000000
+Array :: alias [0b10]u8
+value func() u8 { return 0B101010 }
+length func($N usize) usize { return N }
+main func() i32 {
+	if (value() != 42) return 1
+	if (0o52 != 42 or 0x2a != 42 or 0X2A != 42 or 0O52 != 42) return 2
+	if (maximum != maxval!(u64) or minimum != minval!(i64)) return 3
+	binary_max u64 :: 0b1111111111111111111111111111111111111111111111111111111111111111
+	octal_max u64 :: 0o1777777777777777777777
+	if (binary_max != maximum or octal_max != maximum) return 4
+	items Array :: [0x28, 0b10]
+	if (items.len != 2 or items[0] + items[1] != 42) return 5
+	if (length(0x2A) != 42 or 042 != 42) return 6
+	fraction f64 := 42.5
+	fraction += 0.5
+	if (fraction != 43.0) return 10
+	if (u8(Flags.four) != 4) return 7
+	total := 0
+	for 0b1..0x4 |index| { total += index }
+	if (total != 6) return 8
+	tuple :: {0o50, 0b10}
+	if (tuple.0 + tuple.1 != 42) return 9
+	return 0
+}
+`
+	_ = os2.remove_all(directory)
+	defer _ = os2.remove_all(directory)
+	defer _ = os.remove(output)
+	testing.expect(t, os.make_directory(directory) == nil)
+	testing.expect(t, os.write_entire_file("/tmp/brolang-test-integer-bases/main.bro", transmute([]byte)text))
+	status := compiler_core.compile_package(directory, output)
+	testing.expect_value(t, status, 0)
+	if status != 0 {
+		return
+	}
+	state := run_executable(output)
+	testing.expect_value(t, state.exit_code, 0)
+}
+
+@(test)
+integer_base_literals_reject_invalid_digits_without_losing_following_declarations :: proc(t: ^testing.T) {
+	literals := []string{
+		"0b", "0o", "0x", "0B", "0O", "0X",
+		"0b2", "0b102", "0o8", "0o78", "0xg", "0x1G",
+		"0b1name", "0x_1", "0b10_01",
+	}
+	for literal in literals {
+		text := fmt.aprintf("bad :: %s\nvalid :: 42\n", literal)
+		defer delete(text)
+		source_file := source.Source{path="test.bro", text=text}
+		diagnostics := source.init_diagnostics(&source_file)
+		defer source.destroy_diagnostics(&diagnostics)
+		symbols := symbol.init_table()
+		defer symbol.destroy_table(&symbols)
+		stream := lexer.lex(&source_file, &diagnostics, &symbols)
+		defer delete(stream.items)
+		module := parser.parse(&stream, &source_file, &diagnostics)
+		defer ast.destroy_module(&module)
+		testing.expect_value(t, len(diagnostics.items), 1)
+		if len(diagnostics.items) != 1 || len(module.globals) != 2 {
+			testing.expect_value(t, len(module.globals), 2)
+			continue
+		}
+		testing.expect_value(t, diagnostics.items[0].span.start, source.Offset(7))
+		testing.expect_value(t, diagnostics.items[0].span.end, source.Offset(7+len(literal)))
+		testing.expect_value(t, module.exprs[module.globals[0].expr].kind, ast.Expr_Kind.Invalid)
+		testing.expect_value(t, module.exprs[module.globals[1].expr].integer, u64(42))
+	}
+}
+
+@(test)
+integer_base_literals_check_magnitude_and_keep_tuple_ordinals_decimal :: proc(t: ^testing.T) {
+	cases := []string{
+		"value u64 :: 0x10000000000000000\n",
+		"value u64 :: 0o2000000000000000000000\n",
+		"value u64 :: 0b10000000000000000000000000000000000000000000000000000000000000000\n",
+		"value :: tuple.0b0\n",
+		"value :: tuple.0o0\n",
+		"value :: tuple.0x0\n",
+	}
+	for text in cases {
+		source_file := source.Source{path="test.bro", text=text}
+		diagnostics := source.init_diagnostics(&source_file)
+		defer source.destroy_diagnostics(&diagnostics)
+		symbols := symbol.init_table()
+		defer symbol.destroy_table(&symbols)
+		stream := lexer.lex(&source_file, &diagnostics, &symbols)
+		defer delete(stream.items)
+		module := parser.parse(&stream, &source_file, &diagnostics)
+		defer ast.destroy_module(&module)
+		testing.expect_value(t, len(diagnostics.items), 1)
+		if len(module.globals) == 1 {
+			testing.expect_value(t, module.exprs[module.globals[0].expr].kind, ast.Expr_Kind.Invalid)
+		} else {
+			testing.expect_value(t, len(module.globals), 1)
+		}
+	}
+}
+
+@(test)
+integer_base_literals_reject_overflow_in_array_counts_and_sentinels :: proc(t: ^testing.T) {
+	text := `Array :: alias [0x10000000000000000]u8
+Pointer :: alias [*;0o2000000000000000000000]u8
+Slice :: alias [;0b10000000000000000000000000000000000000000000000000000000000000000]u8
+`
+	source_file := source.Source{path="test.bro", text=text}
+	diagnostics := source.init_diagnostics(&source_file)
+	defer source.destroy_diagnostics(&diagnostics)
+	symbols := symbol.init_table()
+	defer symbol.destroy_table(&symbols)
+	stream := lexer.lex(&source_file, &diagnostics, &symbols)
+	defer delete(stream.items)
+	module := parser.parse(&stream, &source_file, &diagnostics)
+	defer ast.destroy_module(&module)
+	testing.expect_value(t, len(diagnostics.items), 3)
+	for diagnostic in diagnostics.items {
+		// Overflow must identify the complete literal, not its prefix or delimiter.
+		literal := text[int(diagnostic.span.start):int(diagnostic.span.end)]
+		testing.expect(t, literal == "0x10000000000000000" ||
+			literal == "0o2000000000000000000000" ||
+			literal == "0b10000000000000000000000000000000000000000000000000000000000000000")
+	}
+}
+
 @(test)
 parser_marks_only_bang_calls_as_intrinsic :: proc(t: ^testing.T) {
 	text := `main func() void {