diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 288e2b0f97..30c5f791d5 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -8,16 +8,6 @@
 		<!-- Default test suite to run all tests -->
 		<testsuite name="default">
 			<directory suffix=".php">tests/phpunit/tests</directory>
-			<file phpVersion="5.3.0">tests/phpunit/tests/actions/closures.php</file>
-			<file phpVersion="5.3.0">tests/phpunit/tests/image/editor.php</file>
-			<file phpVersion="5.3.0">tests/phpunit/tests/image/editorGd.php</file>
-			<file phpVersion="5.3.0">tests/phpunit/tests/image/editorImagick.php</file>
-			<file phpVersion="5.3.0">tests/phpunit/tests/oembed/headers.php</file>
-			<exclude>tests/phpunit/tests/actions/closures.php</exclude>
-			<exclude>tests/phpunit/tests/image/editor.php</exclude>
-			<exclude>tests/phpunit/tests/image/editorGd.php</exclude>
-			<exclude>tests/phpunit/tests/image/editorImagick.php</exclude>
-			<exclude>tests/phpunit/tests/oembed/headers.php</exclude>
 			<exclude>tests/phpunit/tests/rest-api/rest-autosaves-controller.php</exclude>
 		</testsuite>
 		<!-- Sets the DOING_AUTOSAVE constant, so needs to be run last -->
diff --git a/src/wp-includes/class-wp-customize-manager.php b/src/wp-includes/class-wp-customize-manager.php
index 2636489bea..e1ca84fb15 100644
--- a/src/wp-includes/class-wp-customize-manager.php
+++ b/src/wp-includes/class-wp-customize-manager.php
@@ -1376,13 +1376,6 @@ final class WP_Customize_Manager {
 						)
 					);
 
-					// In PHP < 5.6 filesize() returns 0 for the temp files unless we clear the file status cache.
-					// Technically, PHP < 5.6.0 || < 5.5.13 || < 5.4.29 but no need to be so targeted.
-					// See https://bugs.php.net/bug.php?id=65701
-					if ( version_compare( PHP_VERSION, '5.6', '<' ) ) {
-						clearstatcache();
-					}
-
 					$attachment_id = media_handle_sideload( $file_array, 0, null, $attachment_post_data );
 					if ( is_wp_error( $attachment_id ) ) {
 						continue;
diff --git a/src/wp-includes/class-wp-locale.php b/src/wp-includes/class-wp-locale.php
index 8582964a07..875a061568 100644
--- a/src/wp-includes/class-wp-locale.php
+++ b/src/wp-includes/class-wp-locale.php
@@ -199,13 +199,8 @@ class WP_Locale {
 		/* translators: $thousands_sep argument for https://secure.php.net/number_format, default is ',' */
 		$thousands_sep = __( 'number_format_thousands_sep' );
 
-		if ( version_compare( PHP_VERSION, '5.4', '>=' ) ) {
-			// Replace space with a non-breaking space to avoid wrapping.
-			$thousands_sep = str_replace( ' ', '&nbsp;', $thousands_sep );
-		} else {
-			// PHP < 5.4.0 does not support multiple bytes in thousands separator.
-			$thousands_sep = str_replace( array( '&nbsp;', '&#160;' ), ' ', $thousands_sep );
-		}
+		// Replace space with a non-breaking space to avoid wrapping.
+		$thousands_sep = str_replace( ' ', '&nbsp;', $thousands_sep );
 
 		$this->number_format['thousands_sep'] = ( 'number_format_thousands_sep' === $thousands_sep ) ? ',' : $thousands_sep;
 
diff --git a/src/wp-includes/formatting.php b/src/wp-includes/formatting.php
index feed291794..63397aea5d 100644
--- a/src/wp-includes/formatting.php
+++ b/src/wp-includes/formatting.php
@@ -5572,15 +5572,10 @@ function _print_emoji_detection_script() {
  * @return string The encoded content.
  */
 function wp_encode_emoji( $content ) {
-	$emoji  = _wp_emoji_list( 'partials' );
-	$compat = version_compare( phpversion(), '5.4', '<' );
+	$emoji = _wp_emoji_list( 'partials' );
 
 	foreach ( $emoji as $emojum ) {
-		if ( $compat ) {
-			$emoji_char = html_entity_decode( $emojum, ENT_COMPAT, 'UTF-8' );
-		} else {
-			$emoji_char = html_entity_decode( $emojum );
-		}
+		$emoji_char = html_entity_decode( $emojum );
 		if ( false !== strpos( $content, $emoji_char ) ) {
 			$content = preg_replace( "/$emoji_char/", $emojum, $content );
 		}
@@ -5616,14 +5611,9 @@ function wp_staticize_emoji( $text ) {
 
 	// Quickly narrow down the list of emoji that might be in the text and need replacing.
 	$possible_emoji = array();
-	$compat         = version_compare( phpversion(), '5.4', '<' );
 	foreach ( $emoji as $emojum ) {
 		if ( false !== strpos( $text, $emojum ) ) {
-			if ( $compat ) {
-				$possible_emoji[ $emojum ] = html_entity_decode( $emojum, ENT_COMPAT, 'UTF-8' );
-			} else {
-				$possible_emoji[ $emojum ] = html_entity_decode( $emojum );
-			}
+			$possible_emoji[ $emojum ] = html_entity_decode( $emojum );
 		}
 	}
 
diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index c5f98e5c38..d3dded8078 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -6004,12 +6004,7 @@ function wp_allowed_protocols() {
 function wp_debug_backtrace_summary( $ignore_class = null, $skip_frames = 0, $pretty = true ) {
 	static $truncate_paths;
 
-	if ( version_compare( PHP_VERSION, '5.2.5', '>=' ) ) {
-		$trace = debug_backtrace( false );
-	} else {
-		$trace = debug_backtrace();
-	}
-
+	$trace       = debug_backtrace( false );
 	$caller      = array();
 	$check_class = ! is_null( $ignore_class );
 	$skip_frames++; // skip this function
diff --git a/tests/phpunit/includes/utils.php b/tests/phpunit/includes/utils.php
index a213bce0d0..9a03250f6a 100644
--- a/tests/phpunit/includes/utils.php
+++ b/tests/phpunit/includes/utils.php
@@ -465,12 +465,8 @@ class WpdbExposedMethodsForTesting extends wpdb {
 function benchmark_pcre_backtracking( $pattern, $subject, $strategy ) {
 	$saved_config = ini_get( 'pcre.backtrack_limit' );
 
-	// Attempt to prevent PHP crashes.  Adjust these lower when needed.
-	if ( version_compare( phpversion(), '5.4.8', '>' ) ) {
-		$limit = 1000000;
-	} else {
-		$limit = 20000;  // 20,000 is a reasonable upper limit, but see also https://core.trac.wordpress.org/ticket/29557#comment:10
-	}
+	// Attempt to prevent PHP crashes. Adjust these lower when needed.
+	$limit = 1000000;
 
 	// Start with small numbers, so if a crash is encountered at higher numbers we can still debug the problem.
 	for ( $i = 4; $i <= $limit; $i *= 2 ) {
diff --git a/tests/phpunit/multisite.xml b/tests/phpunit/multisite.xml
index 620b20fc0d..73934a7a90 100644
--- a/tests/phpunit/multisite.xml
+++ b/tests/phpunit/multisite.xml
@@ -12,14 +12,6 @@
 		<!-- Default test suite to run all tests -->
 		<testsuite name="default">
 			<directory suffix=".php">tests</directory>
-			<file phpVersion="5.3.0">tests/phpunit/tests/actions/closures.php</file>
-			<file phpVersion="5.3.0">tests/phpunit/tests/image/editor.php</file>
-			<file phpVersion="5.3.0">tests/phpunit/tests/image/editorGd.php</file>
-			<file phpVersion="5.3.0">tests/phpunit/tests/image/editorImagick.php</file>
-			<exclude>tests/phpunit/tests/actions/closures.php</exclude>
-			<exclude>tests/phpunit/tests/image/editor.php</exclude>
-			<exclude>tests/phpunit/tests/image/editorGd.php</exclude>
-			<exclude>tests/phpunit/tests/image/editorImagick.php</exclude>
 			<!-- Path relative to the checkout root, for PHPUnit 3.6.x -->
 			<exclude>tests/phpunit/tests/rest-api/rest-autosaves-controller.php</exclude>
 			<!-- Same path relative to the configuration file, for PHPUnit 4.0.0+ -->
diff --git a/tests/phpunit/tests/admin/wpPrivacyRequestsTable.php b/tests/phpunit/tests/admin/wpPrivacyRequestsTable.php
index 9c9be20f92..debe163862 100644
--- a/tests/phpunit/tests/admin/wpPrivacyRequestsTable.php
+++ b/tests/phpunit/tests/admin/wpPrivacyRequestsTable.php
@@ -24,10 +24,6 @@ class Tests_Admin_WpPrivacyRequestsTable extends WP_UnitTestCase {
 	 * @return PHPUnit_Framework_MockObject_MockObject|WP_Privacy_Requests_Table $instance Mocked class instance.
 	 */
 	public function get_mocked_class_instance() {
-		if ( version_compare( PHP_VERSION, '5.3', '<' ) ) {
-			$this->markTestSkipped( 'ReflectionMethod::setAccessible is only available in PHP 5.3+' );
-		}
-
 		$args = array(
 			'plural'   => 'privacy_requests',
 			'singular' => 'privacy_request',
diff --git a/tests/phpunit/tests/compat.php b/tests/phpunit/tests/compat.php
index 92cefbf946..dd6e06c0af 100644
--- a/tests/phpunit/tests/compat.php
+++ b/tests/phpunit/tests/compat.php
@@ -249,11 +249,6 @@ EOT;
 			$this->markTestSkipped( 'The intl extension is not loaded. ResourceBundle not tested for is_countable().' );
 		}
 
-		if ( version_compare( PHP_VERSION, '5.4', '<' ) ) {
-			$this->markTestSkipped( 'ResourceBundle is only countable in PHP 5.4+' );
-			return;
-		}
-
 		$this->assertTrue( is_countable( new ResourceBundle( 'en', null ) ) );
 	}
 
diff --git a/tests/phpunit/tests/customize/nav-menus.php b/tests/phpunit/tests/customize/nav-menus.php
index e7387773ac..1de6047097 100644
--- a/tests/phpunit/tests/customize/nav-menus.php
+++ b/tests/phpunit/tests/customize/nav-menus.php
@@ -1083,9 +1083,7 @@ class Test_WP_Customize_Nav_Menus extends WP_UnitTestCase {
 		);
 
 		// Add global namespace prefix to check #41488.
-		if ( version_compare( PHP_VERSION, '5.3', '>=' ) ) {
-			$original_args['fallback_cb'] = '\\' . $original_args['fallback_cb'];
-		}
+		$original_args['fallback_cb'] = '\\' . $original_args['fallback_cb'];
 
 		$args = $menus->filter_wp_nav_menu_args( $original_args );
 
diff --git a/tests/phpunit/tests/db/charset.php b/tests/phpunit/tests/db/charset.php
index 3089ec9a74..dc7f7c3b8f 100644
--- a/tests/phpunit/tests/db/charset.php
+++ b/tests/phpunit/tests/db/charset.php
@@ -482,10 +482,6 @@ class Tests_DB_Charset extends WP_UnitTestCase {
 	 * @ticket 21212
 	 */
 	function test_strip_invalid_text( $data, $expected, $message ) {
-		if ( version_compare( PHP_VERSION, '5.3', '<' ) && stristr( php_uname( 's' ), 'win' ) ) {
-			$this->markTestSkipped( 'This test fails in PHP 5.2 on Windows. See https://core.trac.wordpress.org/ticket/31262' );
-		}
-
 		$charset = self::$_wpdb->charset;
 		if ( isset( $data[0]['connection_charset'] ) ) {
 			$new_charset = $data[0]['connection_charset'];
diff --git a/tests/phpunit/tests/functions.php b/tests/phpunit/tests/functions.php
index 2191af7ddb..dd29c779e5 100644
--- a/tests/phpunit/tests/functions.php
+++ b/tests/phpunit/tests/functions.php
@@ -918,10 +918,6 @@ class Tests_Functions extends WP_UnitTestCase {
 	 * @ticket 28786
 	 */
 	function test_wp_json_encode_depth() {
-		if ( version_compare( PHP_VERSION, '5.5', '<' ) ) {
-			$this->markTestSkipped( 'json_encode() supports the $depth parameter in PHP 5.5+' );
-		};
-
 		$data = array( array( array( 1, 2, 3 ) ) );
 		$json = wp_json_encode( $data, 0, 1 );
 		$this->assertFalse( $json );
diff --git a/tests/phpunit/tests/post/query.php b/tests/phpunit/tests/post/query.php
index 7388dc24b7..4bac94c1bc 100644
--- a/tests/phpunit/tests/post/query.php
+++ b/tests/phpunit/tests/post/query.php
@@ -705,11 +705,6 @@ class Tests_Post_Query extends WP_UnitTestCase {
 	 * @dataProvider set_found_posts_provider
 	 */
 	public function test_set_found_posts_not_posts_as_an_array( $posts, $expected ) {
-		if ( version_compare( PHP_VERSION, '5.3', '<' ) ) {
-			$this->markTestSkipped( 'ReflectionMethod::setAccessible is only available in PHP 5.3+' );
-			return;
-		}
-
 		$q = new WP_Query(
 			array(
 				'post_type'      => 'wptests_pt',
diff --git a/tests/phpunit/tests/rest-api/rest-request.php b/tests/phpunit/tests/rest-api/rest-request.php
index cf3d79142c..2dd539a509 100644
--- a/tests/phpunit/tests/rest-api/rest-request.php
+++ b/tests/phpunit/tests/rest-api/rest-request.php
@@ -491,10 +491,6 @@ class Tests_REST_Request extends WP_UnitTestCase {
 	}
 
 	public function test_has_valid_params_json_error() {
-		if ( version_compare( PHP_VERSION, '5.3', '<' ) ) {
-			return $this->markTestSkipped( 'JSON validation is only available for PHP 5.3+' );
-		}
-
 		$this->request->set_header( 'Content-Type', 'application/json' );
 		$this->request->set_body( '{"invalid": JSON}' );
 
@@ -507,10 +503,6 @@ class Tests_REST_Request extends WP_UnitTestCase {
 
 
 	public function test_has_valid_params_empty_json_no_error() {
-		if ( version_compare( PHP_VERSION, '5.3', '<' ) ) {
-			return $this->markTestSkipped( 'JSON validation is only available for PHP 5.3+' );
-		}
-
 		$this->request->set_header( 'Content-Type', 'application/json' );
 		$this->request->set_body( '' );
 
diff --git a/tests/phpunit/tests/theme/customHeader.php b/tests/phpunit/tests/theme/customHeader.php
index eeb240fc91..65b037042a 100644
--- a/tests/phpunit/tests/theme/customHeader.php
+++ b/tests/phpunit/tests/theme/customHeader.php
@@ -126,10 +126,6 @@ class Tests_Theme_Custom_Header extends WP_UnitTestCase {
 		$this->assertFalse( has_custom_header() );
 		$this->assertEmpty( $html );
 
-		// ReflectionMethod::setAccessible is only available in PHP 5.3+
-		if ( version_compare( PHP_VERSION, '5.3', '<' ) ) {
-			return;
-		}
 		// The container should always be returned in the Customizer preview.
 		$this->_set_customize_previewing( true );
 		$html = get_custom_header_markup();
@@ -226,11 +222,6 @@ class Tests_Theme_Custom_Header extends WP_UnitTestCase {
 	}
 
 	function test_header_script_is_enqueued_by_the_custom_header_markup_without_video_when_previewing_in_customizer() {
-		if ( version_compare( PHP_VERSION, '5.3', '<' ) ) {
-			$this->markTestSkipped( 'ReflectionMethod::setAccessible is only available in PHP 5.3+' );
-			return;
-		}
-
 		$this->_add_theme_support(
 			array(
 				'video'                 => true,
diff --git a/tests/phpunit/tests/widgets/media-widget.php b/tests/phpunit/tests/widgets/media-widget.php
index 86a06eccc6..6b9dc926ce 100644
--- a/tests/phpunit/tests/widgets/media-widget.php
+++ b/tests/phpunit/tests/widgets/media-widget.php
@@ -479,11 +479,6 @@ class Test_WP_Widget_Media extends WP_UnitTestCase {
 	 * @covers WP_Widget_Media::has_content()
 	 */
 	function test_has_content() {
-		if ( version_compare( PHP_VERSION, '5.3', '<' ) ) {
-			$this->markTestSkipped( 'ReflectionMethod::setAccessible is only available for PHP 5.3+' );
-			return;
-		}
-
 		$attachment_id = self::factory()->attachment->create_object(
 			array(
 				'file'           => DIR_TESTDATA . '/images/canola.jpg',