diff --git a/src/Psl/Arr/filter.php b/src/Psl/Arr/filter.php
new file mode 100644
index 0000000..58a6082
--- /dev/null
+++ b/src/Psl/Arr/filter.php
@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Psl\Arr;
+
+use Closure;
+
+/**
+ * Returns an array containing only the values for which the given predicate
+ * returns `true`.
+ *
+ * The default predicate is casting the value to boolean.
+ *
+ * Example:
+ *
+ *      Arr\filter(['', '0', 'a', 'b'])
+ *      => Arr('a', 'b')
+ *
+ *      Arr\filter(['foo', 'bar', 'baz', 'qux'], fn(string $value): bool => Str\contains($value, 'a'));
+ *      => Arr('bar', 'baz')
+ *
+ * @psalm-template Tk of array-key
+ * @psalm-template Tv
+ *
+ * @psalm-param array<Tk, Tv>                   $array
+ * @psalm-param (pure-callable(Tv): bool)|null  $predicate
+ *
+ * @psalm-return array<Tk, Tv>
+ *
+ * @psalm-pure
+ */
+function filter(array $array, ?callable $predicate = null): array
+{
+    /** @psalm-var (pure-callable(Tv): bool) $predicate */
+    $predicate = $predicate ?? Closure::fromCallable('Psl\Internal\boolean');
+    $result = [];
+    foreach ($array as $k => $v) {
+        if ($predicate($v)) {
+            $result[$k] = $v;
+        }
+    }
+
+    return $result;
+}
diff --git a/src/Psl/Arr/filter_keys.php b/src/Psl/Arr/filter_keys.php
new file mode 100644
index 0000000..efe6e9b
--- /dev/null
+++ b/src/Psl/Arr/filter_keys.php
@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Psl\Arr;
+
+use Closure;
+
+/**
+ * Returns an array containing only the keys for which the given predicate
+ * returns `true`.
+ *
+ * The default predicate is casting the key to boolean.
+ *
+ * Example:
+ *
+ *      Arr\filter_keys([0 => 'a', 1 => 'b'])
+ *      => Arr(1 => 'b')
+ *
+ *      Arr\filter_keys([0 => 'a', 1 => 'b', 2 => 'c'], fn(int $key): bool => $key <= 1);
+ *      => Arr(0 => 'a', 1 => 'b')
+ *
+ * @psalm-template Tk of array-key
+ * @psalm-template Tv
+ *
+ * @psalm-param array<Tk, Tv>                   $array
+ * @psalm-param (pure-callable(Tk): bool)|null  $predicate
+ *
+ * @psalm-return array<Tk, Tv>
+ *
+ * @psalm-pure
+ */
+function filter_keys(array $array, ?callable $predicate = null): array
+{
+    /** @psalm-var (pure-callable(Tk): bool) $predicate */
+    $predicate = $predicate ?? Closure::fromCallable('Psl\Internal\boolean');
+    $result = [];
+    foreach ($array as $k => $v) {
+        if ($predicate($k)) {
+            $result[$k] = $v;
+        }
+    }
+
+    return $result;
+}
diff --git a/src/Psl/Arr/filter_nulls.php b/src/Psl/Arr/filter_nulls.php
new file mode 100644
index 0000000..8ae58af
--- /dev/null
+++ b/src/Psl/Arr/filter_nulls.php
@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Psl\Arr;
+
+/**
+ * Filter out null values from the given array.
+ *
+ * Example:
+ *      Arr\filter_nulls([1, null, 5])
+ *      => Arr(1, 5)
+ *
+ * @psalm-template T
+ *
+ * @psalm-param list<T|null> $array
+ *
+ * @psalm-return list<T>
+ *
+ * @psalm-pure
+ */
+function filter_nulls(array $array): array
+{
+    /** @psalm-var list<T> $result */
+    $result = [];
+    foreach ($array as $value) {
+        if (null !== $value) {
+            $result[] = $value;
+        }
+    }
+
+    return $result;
+}
diff --git a/src/Psl/Arr/filter_with_key.php b/src/Psl/Arr/filter_with_key.php
new file mode 100644
index 0000000..2fd1385
--- /dev/null
+++ b/src/Psl/Arr/filter_with_key.php
@@ -0,0 +1,56 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Psl\Arr;
+
+use Psl;
+
+/**
+ * Returns an array containing only the keys and values for which the given predicate
+ * returns `true`.
+ *
+ * The default predicate is casting both they key and the value to boolean.
+ *
+ * Example:
+ *
+ *      Arr\filter_with_key(['a', '0', 'b', 'c'])
+ *      => Iter('b', 'c')
+ *
+ *      Arr\filter_with_key(
+ *          ['foo', 'bar', 'baz', 'qux'],
+ *          fn(int $key, string $value): bool => $key > 1 && Str\contains($value, 'a')
+ *      );
+ *      => Arr('baz')
+ *
+ * @psalm-template Tk of array-key
+ * @psalm-template Tv
+ *
+ * @psalm-param array<Tk, Tv>                       $array
+ * @psalm-param (pure-callable(Tk, Tv): bool)|null  $predicate
+ *
+ * @psalm-return array<Tk, Tv>
+ *
+ * @psalm-pure
+ */
+function filter_with_key(array $array, ?callable $predicate = null): array
+{
+    $predicate = $predicate ??
+        /**
+         * @psalm-param Tk $k
+         * @psalm-param Tv $v
+         *
+         * @psalm-pure
+         */
+        fn ($k, $v): bool => Psl\Internal\boolean($v);
+
+    /** @psalm-var array<Tk, Tv> $result */
+    $result = [];
+    foreach ($array as $k => $v) {
+        if ($predicate($k, $v)) {
+            $result[$k] = $v;
+        }
+    }
+
+    return $result;
+}
diff --git a/src/Psl/Internal/Loader.php b/src/Psl/Internal/Loader.php
index 22d55b8..d549dc6 100644
--- a/src/Psl/Internal/Loader.php
+++ b/src/Psl/Internal/Loader.php
@@ -86,6 +86,10 @@ final class Loader
         'Psl\Arr\slice',
         'Psl\Arr\take',
         'Psl\Arr\take_while',
+        'Psl\Arr\filter',
+        'Psl\Arr\filter_keys',
+        'Psl\Arr\filter_nulls',
+        'Psl\Arr\filter_with_key',
         'Psl\Asio\wrap',
         'Psl\Internal\boolean',
         'Psl\Internal\type',
diff --git a/tests/Psl/Arr/FilterKeysTest.php b/tests/Psl/Arr/FilterKeysTest.php
new file mode 100644
index 0000000..c739490
--- /dev/null
+++ b/tests/Psl/Arr/FilterKeysTest.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Psl\Tests\Arr;
+
+use PHPUnit\Framework\TestCase;
+use Psl\Arr;
+
+class FilterKeysTest extends TestCase
+{
+    /**
+     * @dataProvider provideData
+     */
+    public function testFilterKeys(array $expected, array $array, ?callable $predicate = null): void
+    {
+        $result = Arr\filter_keys($array, $predicate);
+
+        self::assertSame($expected, $result);
+    }
+
+    public function provideData(): iterable
+    {
+        yield  [[], []];
+        yield  [[1 => 'b'], ['a', 'b']];
+        yield  [[], ['a', 'b'], fn () => false];
+        yield  [['a', 'b'], ['a', 'b'], fn (int $_): bool => true];
+        yield  [['a'], ['a', 'b'], fn (int $k): bool => 1 !== $k];
+    }
+}
diff --git a/tests/Psl/Arr/FilterNullsTest.php b/tests/Psl/Arr/FilterNullsTest.php
new file mode 100644
index 0000000..0dfffb1
--- /dev/null
+++ b/tests/Psl/Arr/FilterNullsTest.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Psl\Tests\Arr;
+
+use PHPUnit\Framework\TestCase;
+use Psl\Arr;
+
+class FilterNullsTest extends TestCase
+{
+    public function testFilterNulls(): void
+    {
+        self::assertCount(0, Arr\filter_nulls([]));
+        self::assertCount(0, Arr\filter_nulls([null, null]));
+        self::assertCount(1, Arr\filter_nulls([null, false]));
+        self::assertCount(1, Arr\filter_nulls([null, 'null']));
+        self::assertCount(1, Arr\filter_nulls(['null']));
+    }
+}
diff --git a/tests/Psl/Arr/FilterTest.php b/tests/Psl/Arr/FilterTest.php
new file mode 100644
index 0000000..2336bb7
--- /dev/null
+++ b/tests/Psl/Arr/FilterTest.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Psl\Tests\Arr;
+
+use PHPUnit\Framework\TestCase;
+use Psl\Arr;
+
+class FilterTest extends TestCase
+{
+    /**
+     * @dataProvider provideData
+     */
+    public function testFilter(array $expected, array $array, ?callable $predicate = null): void
+    {
+        $result = Arr\filter($array, $predicate);
+
+        self::assertSame($expected, $result);
+    }
+
+    public function provideData(): iterable
+    {
+        yield  [[], []];
+        yield  [['a', 'b'], ['a', 'b']];
+        yield  [[], ['a', 'b'], fn () => false];
+        yield  [['a', 'b'], ['a', 'b'], fn (string $_): bool => true];
+        yield  [['a'], ['a', 'b'], fn (string $v): bool => 'b' !== $v];
+    }
+}
diff --git a/tests/Psl/Arr/FilterWithKeyTest.php b/tests/Psl/Arr/FilterWithKeyTest.php
new file mode 100644
index 0000000..095c74d
--- /dev/null
+++ b/tests/Psl/Arr/FilterWithKeyTest.php
@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Psl\Tests\Arr;
+
+use PHPUnit\Framework\TestCase;
+use Psl\Arr;
+
+class FilterWithKeyTest extends TestCase
+{
+    /**
+     * @dataProvider provideData
+     */
+    public function testFilterWithKey(array $expected, array $array, ?callable $predicate = null): void
+    {
+        $result = Arr\filter_with_key($array, $predicate);
+
+        self::assertSame($expected, $result);
+    }
+
+    public function provideData(): iterable
+    {
+        yield  [[], []];
+        yield  [['a', 'b'], ['a', 'b']];
+        yield  [[], ['a', 'b'], fn (int $_k, string $_v) => false];
+        yield  [['a', 'b'], ['a', 'b'], fn (int $_k, string $_v): bool => true];
+        yield  [['a'], ['a', 'b'], fn (int $k, string $v): bool => 'b' !== $v];
+        yield  [[], ['a', 'b'], fn (int $k, string $v): bool => 'b' !== $v && 0 !== $k];
+        yield  [['a'], ['a', 'b'], fn (int $k, string $v): bool => 'b' !== $v && 1 !== $k];
+        yield  [[], ['a', 'b'], fn (int $k, string $v): bool => 'a' !== $v && 1 !== $k];
+        yield  [[1 => 'b'], ['a', 'b'], fn (int $k, string $v): bool => 'a' !== $v && 0 !== $k];
+    }
+}