diff --git a/.github/workflows/test-all.yaml b/.github/workflows/test-all.yaml
index 3d4aa3fed..71b7bee73 100644
--- a/.github/workflows/test-all.yaml
+++ b/.github/workflows/test-all.yaml
@@ -44,7 +44,6 @@ jobs:
         baseImage:
           [
             "ubuntu:jammy",
-            "debian:11",
             "debian:12",
             "mcr.microsoft.com/devcontainers/base:ubuntu",
             "mcr.microsoft.com/devcontainers/base:debian",
diff --git a/.github/workflows/test-pr-arm64.yaml b/.github/workflows/test-pr-arm64.yaml
index 0de1f066b..758586389 100644
--- a/.github/workflows/test-pr-arm64.yaml
+++ b/.github/workflows/test-pr-arm64.yaml
@@ -36,7 +36,7 @@ jobs:
         features: ${{ fromJSON(needs.detect-changes.outputs.features) }}
         # NOTE: ubuntu:focal and debian:11 are excluded because they ship
         # GLIBC 2.31, but PowerShell >= 7.6.0 requires GLIBC 2.33+ on arm64.
-        # ubuntu:focal reached EOL Apr 2025; debian:11 reaches EOL Aug 2026.
+        # ubuntu:focal reached EOL Apr 2025; debian:11 reached EOL Aug 2026.
         baseImage:
           [
             "ubuntu:jammy",
diff --git a/.github/workflows/test-pr.yaml b/.github/workflows/test-pr.yaml
index e18291f09..ecc96afbb 100644
--- a/.github/workflows/test-pr.yaml
+++ b/.github/workflows/test-pr.yaml
@@ -51,7 +51,6 @@ jobs:
         baseImage:
           [
             "ubuntu:jammy",
-            "debian:11",
             "debian:12",
             "mcr.microsoft.com/devcontainers/base:ubuntu",
             "mcr.microsoft.com/devcontainers/base:debian",
diff --git a/test/anaconda/install_anaconda_bullseye.sh b/test/anaconda/install_anaconda_bullseye.sh
deleted file mode 100644
index 4a17f3dc1..000000000
--- a/test/anaconda/install_anaconda_bullseye.sh
+++ /dev/null
@@ -1,30 +0,0 @@
-#!/bin/bash
-
-set -e
-
-# Optional: Import test library
-source dev-container-features-test-lib
-
-# Definition specific tests
-check "conda" conda --version
-check "python" python --version
-check "pylint" pylint --version
-check "flake8" flake8 --version
-check "autopep8" autopep8 --version
-check "yapf" yapf --version
-check "pydocstyle" pydocstyle --version
-check "pycodestyle" pycodestyle --version
-check "if conda-notice.txt exists" cat /usr/local/etc/vscode-dev-containers/conda-notice.txt
-
-check "certifi" pip show certifi | grep Version
-check "cryptography" pip show cryptography | grep Version
-check "setuptools" pip show setuptools | grep Version
-check "tornado" pip show tornado | grep Version
-
-check "conda-update-conda" bash -c "conda update -y conda"
-check "conda-install-tensorflow" bash -c "conda create --name test-env -c conda-forge --yes tensorflow"
-check "conda-install-pytorch" bash -c "conda create --name test-env -c conda-forge --yes pytorch"
-
-# Report result
-reportResults
-
diff --git a/test/anaconda/scenarios.json b/test/anaconda/scenarios.json
index 65fba8458..de975e7d3 100644
--- a/test/anaconda/scenarios.json
+++ b/test/anaconda/scenarios.json
@@ -26,15 +26,6 @@
       }
     }
    },
-   "install_anaconda_bullseye": {
-    "image": "mcr.microsoft.com/devcontainers/base:bullseye",
-    "user": "vscode",
-    "features": {
-      "anaconda": {
-        "version": "latest"
-      }
-    }
-  },
   "install_anaconda_noble_without_user": {
     "image": "mcr.microsoft.com/devcontainers/base:noble",
     "features": {
diff --git a/test/azure-cli/install_using_python_with_python_3_11_bullseye.sh b/test/azure-cli/install_using_python_with_python_3_11_bookworm.sh
similarity index 70%
rename from test/azure-cli/install_using_python_with_python_3_11_bullseye.sh
rename to test/azure-cli/install_using_python_with_python_3_11_bookworm.sh
index b9957843e..074876148 100644
--- a/test/azure-cli/install_using_python_with_python_3_11_bullseye.sh
+++ b/test/azure-cli/install_using_python_with_python_3_11_bookworm.sh
@@ -10,10 +10,10 @@ check "user is vscode" whoami | grep vscode
 check "version" az  --version
 
 echo -e "\n\n🔄 Testing 'O.S'"
-if cat /etc/os-release | grep -q 'PRETTY_NAME="Debian GNU/Linux 11 (bullseye)"'; then
-    echo -e "\n\n✅ Passed 'O.S is Linux 11 (bullseye)'!"
+if cat /etc/os-release | grep -q 'PRETTY_NAME="Debian GNU/Linux 12 (bookworm)"'; then
+    echo -e "\n\n✅ Passed 'O.S is Linux 12 (bookworm)'!"
 else
-    echo -e "\n\n❌ Failed 'O.S is other than Linux 11 (bullseye)'!"
+    echo -e "\n\n❌ Failed 'O.S is other than Linux 12 (bookworm)'!"
 fi
 
 
diff --git a/test/azure-cli/scenarios.json b/test/azure-cli/scenarios.json
index 29fb4f935..15786177a 100644
--- a/test/azure-cli/scenarios.json
+++ b/test/azure-cli/scenarios.json
@@ -86,8 +86,8 @@
       }
     }
   },
-  "install_using_python_with_python_3_11_bullseye": {
-    "image": "mcr.microsoft.com/devcontainers/python:1-3.11-bullseye",
+  "install_using_python_with_python_3_11_bookworm": {
+    "image": "mcr.microsoft.com/devcontainers/python:1-3.11-bookworm",
     "user": "vscode",
     "features": {
       "azure-cli": {
diff --git a/test/common-utils/bullseye.sh b/test/common-utils/bullseye.sh
deleted file mode 100755
index 5a396a7f4..000000000
--- a/test/common-utils/bullseye.sh
+++ /dev/null
@@ -1,14 +0,0 @@
-#!/bin/bash
-
-set -e
-
-# Optional: Import test library
-source dev-container-features-test-lib
-
-# Definition specific tests
-. /etc/os-release
-check "non-root user" test "$(whoami)" = "devcontainer"
-check "distro" test "${VERSION_CODENAME}" = "bullseye"
-
-# Report result
-reportResults
\ No newline at end of file
diff --git a/test/common-utils/scenarios.json b/test/common-utils/scenarios.json
index c70c574a7..98f73d1eb 100644
--- a/test/common-utils/scenarios.json
+++ b/test/common-utils/scenarios.json
@@ -13,13 +13,6 @@
             "common-utils": {}
         }
     },    
-    "bullseye": {
-        "image": "debian:bullseye",
-        "remoteUser": "devcontainer",
-        "features": {
-            "common-utils": {}
-        }
-    },
     "bookworm": {
         "image": "debian:bookworm",
         "remoteUser": "devcontainer",
@@ -114,7 +107,7 @@
         }
     },
     "alternate-values": {
-        "image": "debian:bullseye",
+        "image": "debian:bookworm",
         "features": {
             "common-utils": {
                 "username": "alternate",
@@ -127,7 +120,7 @@
         }
     },
     "username-default": {
-        "image": "debian:bullseye",
+        "image": "debian:bookworm",
         "features": {
             "common-utils": {}
         }
@@ -166,7 +159,7 @@
         }
     },
     "configure_zsh_no_template_first_step": {
-        "image": "debian:bullseye",
+        "image": "debian:bookworm",
         "remoteUser": "devcontainer",
         "features": {
             "common-utils": {
diff --git a/test/git/install_git_from_src_bullseye.sh b/test/git/install_git_from_src_bullseye.sh
deleted file mode 100644
index 6a1f639cf..000000000
--- a/test/git/install_git_from_src_bullseye.sh
+++ /dev/null
@@ -1,17 +0,0 @@
-#!/bin/bash
-
-set -e
-
-# Optional: Import test library
-source dev-container-features-test-lib
-
-# Definition specific tests
-check "version" git  --version
-check "gettext" dpkg-query -l gettext
-
-cd /tmp && git clone https://github.com/devcontainers/feature-starter.git
-cd feature-starter
-check "perl" bash -c "git -c grep.patternType=perl grep -q 'a.+b'"
-
-# Report result
-reportResults
diff --git a/test/git/scenarios.json b/test/git/scenarios.json
index d47f0bb6e..ffa3c0c2f 100644
--- a/test/git/scenarios.json
+++ b/test/git/scenarios.json
@@ -71,15 +71,6 @@
             }
         }
     },
-    "install_git_from_src_bullseye": {
-        "image": "debian:bullseye",
-        "features": {
-            "git": {
-                "version": "latest",
-                "ppa": "false"
-            }
-        }
-    },
     "install_git_from_src_bookworm": {
         "image": "debian:bookworm",
         "features": {
diff --git a/test/java/scenarios.json b/test/java/scenarios.json
index aedd17cad..fe6ef9137 100644
--- a/test/java/scenarios.json
+++ b/test/java/scenarios.json
@@ -9,7 +9,7 @@
         }
     },
     "install_maven_specific_version_no_java": {
-        "image": "mcr.microsoft.com/devcontainers/java:1-8-bullseye",
+        "image": "mcr.microsoft.com/devcontainers/java:1-17-bookworm",
         "features": {
             "java": {
                 "version": "none",
diff --git a/test/node/scenarios.json b/test/node/scenarios.json
index 9459d0e4a..22f20bb48 100644
--- a/test/node/scenarios.json
+++ b/test/node/scenarios.json
@@ -16,7 +16,7 @@
         }
     },
     "nvm_test_fallback": {
-        "image": "debian:11",
+        "image": "debian:12",
         "features": {
             "node": {
                 "version": "lts"
@@ -24,7 +24,7 @@
         }
     },
     "install_additional_node": {
-        "image": "debian:11",
+        "image": "debian:12",
         "features": {
             "node": {
                 "version": "lts",
diff --git a/test/python/scenarios.json b/test/python/scenarios.json
index a489ee8e6..ac412dff2 100644
--- a/test/python/scenarios.json
+++ b/test/python/scenarios.json
@@ -110,7 +110,7 @@
         }
     },
     "install_os_provided_python_deb": {
-        "image": "mcr.microsoft.com/devcontainers/base:1-bullseye",
+        "image": "mcr.microsoft.com/devcontainers/base:1-bookworm",
         "features": {
             "python": "os-provided"
         }
@@ -128,7 +128,7 @@
         }
     },
     "install_jupyterlab_from_python_image": {
-        "image": "mcr.microsoft.com/devcontainers/python:3.10-bullseye",
+        "image": "mcr.microsoft.com/devcontainers/python:3.10-bookworm",
         "remoteUser": "vscode",
         "features": {
             "python": {
@@ -139,13 +139,13 @@
         }
     },
     "install_via_oryx": {
-        "image": "mcr.microsoft.com/oryx/build:full-debian-bullseye",
+        "image": "mcr.microsoft.com/oryx/build:github-actions-debian-bookworm",
         "features": {
             "python": "3.10"
         }
     },
     "install_jupyterlab_debian": {
-        "image": "debian:bullseye-slim",
+        "image": "debian:bookworm-slim",
         "features": {
             "python": {
                 "version": "3.11",