diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 90adc16..eb6ae59 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -15,7 +15,6 @@ jobs:
     strategy:
       matrix:
         php-version:
-          - '7.3'
           - '7.4'
           - '8.0'
           - '8.1'
diff --git a/README.md b/README.md
index 0159980..b706f55 100644
--- a/README.md
+++ b/README.md
@@ -37,7 +37,7 @@ Installation instructions to use the `composer` command can be found on https://
 
 ### Requirements
 
-PHP Curl Class works with PHP 8.3, 8.2, 8.1, 8.0, 7.4, and 7.3.
+PHP Curl Class works with PHP 8.3, 8.2, 8.1, 8.0, and 7.4.
 
 ### Quick Start and Examples
 
diff --git a/composer.json b/composer.json
index 141175c..3f8181c 100644
--- a/composer.json
+++ b/composer.json
@@ -18,7 +18,7 @@
         }
     ],
     "require": {
-        "php": ">=7.3",
+        "php": ">=7.4",
         "ext-curl": "*"
     },
     "require-dev": {
diff --git a/tests/check_coding_standards.sh b/tests/check_coding_standards.sh
index 51e7f89..b1ab3a6 100755
--- a/tests/check_coding_standards.sh
+++ b/tests/check_coding_standards.sh
@@ -115,12 +115,9 @@ if [[ "${?}" -ne 0 ]]; then
 fi
 
 # Run PHP-CS-Fixer.
-if   [[ "${CI_PHP_VERSION}" == "7.3" ]]; then :
-else
-    vendor/bin/php-cs-fixer --version
-    vendor/bin/php-cs-fixer fix --ansi --config="tests/.php-cs-fixer.php" --diff --dry-run
-    if [[ "${?}" -ne 0 ]]; then
-        echo "Error: found PHP-CS-Fixer coding standard violation(s)"
-        errors+=("found PHP-CS-Fixer coding standard violation(s)")
-    fi
+vendor/bin/php-cs-fixer --version
+vendor/bin/php-cs-fixer fix --ansi --config="tests/.php-cs-fixer.php" --diff --dry-run
+if [[ "${?}" -ne 0 ]]; then
+    echo "Error: found PHP-CS-Fixer coding standard violation(s)"
+    errors+=("found PHP-CS-Fixer coding standard violation(s)")
 fi
diff --git a/tests/dockerfiles/php73/1_build.sh b/tests/dockerfiles/php73/1_build.sh
deleted file mode 100755
index 4cb42d3..0000000
--- a/tests/dockerfiles/php73/1_build.sh
+++ /dev/null
@@ -1,3 +0,0 @@
-# Build an image.
-set -x
-docker build --tag="php-curl-class/php73" .
diff --git a/tests/dockerfiles/php73/2_start.sh b/tests/dockerfiles/php73/2_start.sh
deleted file mode 100755
index de2a49b..0000000
--- a/tests/dockerfiles/php73/2_start.sh
+++ /dev/null
@@ -1,15 +0,0 @@
-# Run image to create container.
-
-SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-set -x
-cd "${SCRIPT_DIR}/../../.."
-project_dir="${PWD}"
-
-docker start "php73" ||
-    docker run \
-        --detach \
-        --interactive \
-        --mount "type=bind,src=${project_dir},dst=/data,readonly=true" \
-        --name="php73" \
-        --tty \
-        "php-curl-class/php73"
diff --git a/tests/dockerfiles/php73/3_test.sh b/tests/dockerfiles/php73/3_test.sh
deleted file mode 100755
index 3ce53c2..0000000
--- a/tests/dockerfiles/php73/3_test.sh
+++ /dev/null
@@ -1,17 +0,0 @@
-# Run tests inside container.
-command=$(cat <<-END
-mkdir --parents "/tmp/php-curl-class" &&
-rsync --delete --exclude=".git" --exclude="vendor" --exclude="composer.lock" --links --recursive "/data/" "/tmp/php-curl-class/" &&
-cd "/tmp/php-curl-class" &&
-export CI_PHP_VERSION="7.3" &&
-(
-    [ ! -f "/tmp/.composer_updated" ] &&
-    composer --no-interaction update &&
-    touch "/tmp/.composer_updated" ||
-    exit 0
-) &&
-bash "tests/run.sh"
-END
-)
-set -x
-docker exec --tty "php73" sh -c "${command}"
diff --git a/tests/dockerfiles/php73/4_stop.sh b/tests/dockerfiles/php73/4_stop.sh
deleted file mode 100755
index e119c63..0000000
--- a/tests/dockerfiles/php73/4_stop.sh
+++ /dev/null
@@ -1,3 +0,0 @@
-# Stop container.
-set -x
-docker stop "php73"
diff --git a/tests/dockerfiles/php73/Dockerfile b/tests/dockerfiles/php73/Dockerfile
deleted file mode 100644
index ab796d7..0000000
--- a/tests/dockerfiles/php73/Dockerfile
+++ /dev/null
@@ -1,19 +0,0 @@
-FROM php:7.3-cli
-ENV DEBIAN_FRONTEND noninteractive
-
-RUN apt-get --assume-yes --quiet update
-
-RUN apt-get --assume-yes --quiet install git && \
-    apt-get --assume-yes --quiet install libpng-dev && \
-    apt-get --assume-yes --quiet install rsync && \
-    apt-get --assume-yes --quiet install zip
-
-RUN curl --silent --show-error "https://getcomposer.org/installer" | php && \
-    mv "composer.phar" "/usr/local/bin/composer" && \
-    composer global require --no-interaction "phpunit/phpunit"
-
-RUN docker-php-ext-configure gd && \
-    docker-php-ext-install gd
-
-ENV PATH /root/.composer/vendor/bin:$PATH
-CMD ["bash"]
diff --git a/tests/dockerfiles/php73/attach.sh b/tests/dockerfiles/php73/attach.sh
deleted file mode 100755
index f8ef94c..0000000
--- a/tests/dockerfiles/php73/attach.sh
+++ /dev/null
@@ -1,3 +0,0 @@
-# Attach to running container.
-
-docker exec --interactive --tty "php73" bash -l
diff --git a/tests/dockerfiles/php73/run.sh b/tests/dockerfiles/php73/run.sh
deleted file mode 100755
index ced63cf..0000000
--- a/tests/dockerfiles/php73/run.sh
+++ /dev/null
@@ -1,23 +0,0 @@
-bash "1_build.sh"
-if [[ $? -ne 0 ]]; then
-    echo "Error: Build failed"
-    exit 1
-fi
-
-bash "2_start.sh"
-if [[ $? -ne 0 ]]; then
-    echo "Error: Start failed"
-    exit 1
-fi
-
-bash "3_test.sh"
-if [[ $? -ne 0 ]]; then
-    echo "Error: Test failed"
-    exit 1
-fi
-
-bash "4_stop.sh"
-if [[ $? -ne 0 ]]; then
-    echo "Error: Stop failed"
-    exit 1
-fi
diff --git a/tests/dockerfiles/php73/run_interactive.sh b/tests/dockerfiles/php73/run_interactive.sh
deleted file mode 100755
index b7410b5..0000000
--- a/tests/dockerfiles/php73/run_interactive.sh
+++ /dev/null
@@ -1,14 +0,0 @@
-# Run image to create container and attach to it.
-
-SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-set -x
-cd "${SCRIPT_DIR}/../../.."
-project_dir="${PWD}"
-
-docker run \
-    --interactive \
-    --mount "type=bind,src=${project_dir},dst=/data,readonly=true" \
-    --name="php73" \
-    --rm \
-    --tty \
-    "php-curl-class/php73" /bin/bash