diff --git a/core/Makefile b/core/Makefile
index fe33196..8a0621e 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -517,6 +517,15 @@
 
 INSTALLED_BOOTIMAGE_TARGET := $(PRODUCT_OUT)/boot.img
 
+# BOARD_USES_RECOVERY_AS_BOOT = true must have BOARD_BUILD_SYSTEM_ROOT_IMAGE = true.
+ifeq ($(BOARD_USES_RECOVERY_AS_BOOT),true)
+ifneq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE),true)
+  $(error BOARD_BUILD_SYSTEM_ROOT_IMAGE must be enabled for BOARD_USES_RECOVERY_AS_BOOT.)
+endif
+endif
+
+# We build recovery as boot image if BOARD_USES_RECOVERY_AS_BOOT is true.
+ifneq ($(BOARD_USES_RECOVERY_AS_BOOT),true)
 ifeq ($(TARGET_BOOTIMAGE_USE_EXT2),true)
 $(error TARGET_BOOTIMAGE_USE_EXT2 is not supported anymore)
 else ifeq (true,$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_BOOT_SIGNER)) # TARGET_BOOTIMAGE_USE_EXT2 != true
@@ -563,6 +572,7 @@
 	$(hide) $(call assert-max-image-size,$(INSTALLED_BOOTIMAGE_TARGET),$(BOARD_BOOTIMAGE_PARTITION_SIZE))
 
 endif # TARGET_BOOTIMAGE_USE_EXT2
+endif # BOARD_USES_RECOVERY_AS_BOOT
 
 else	# TARGET_NO_KERNEL
 # HACK: The top-level targets depend on the bootimage.  Not all targets
@@ -781,6 +791,8 @@
 $(if $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_VBOOT),$(hide) echo "vboot_subkey=$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_VBOOT_SIGNING_SUBKEY)" >> $(1))
 $(if $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_VBOOT),$(hide) echo "futility=$(FUTILITY)" >> $(1))
 $(if $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_VBOOT),$(hide) echo "vboot_signer_cmd=$(VBOOT_SIGNER)" >> $(1))
+$(if $(filter true,$(BOARD_USES_RECOVERY_AS_BOOT)),\
+    $(hide) echo "recovery_as_boot=true" >> $(1))
 $(if $(filter true,$(BOARD_BUILD_SYSTEM_ROOT_IMAGE)),\
     $(hide) echo "system_root_image=true" >> $(1);\
     echo "ramdisk_dir=$(TARGET_ROOT_OUT)" >> $(1))
@@ -790,7 +802,8 @@
 # -----------------------------------------------------------------
 # Recovery image
 
-ifdef INSTALLED_RECOVERYIMAGE_TARGET
+# Recovery image exists if we are building recovery, or building recovery as boot.
+ifneq (,$(INSTALLED_RECOVERYIMAGE_TARGET)$(filter true,$(BOARD_USES_RECOVERY_AS_BOOT)))
 
 INTERNAL_RECOVERYIMAGE_FILES := $(filter $(TARGET_RECOVERY_OUT)/%, \
     $(ALL_DEFAULT_INSTALLED_MODULES))
@@ -840,12 +853,22 @@
 recovery_fstab := $(strip $(wildcard $(TARGET_DEVICE_DIR)/recovery.fstab))
 endif
 
-ifneq ($(BOARD_USES_FULL_RECOVERY_IMAGE),true)
+# Prior to A/B update, we used to have:
+#   boot.img + recovery-from-boot.p + recovery-resource.dat = recovery.img.
+# recovery-resource.dat is needed only if we carry a patch of the boot and
+# recovery images and invoke install-recovery.sh on the first boot post an
+# OTA update.
+#
+# We no longer need that if one of the following conditions holds:
+#   a) We carry a full copy of the recovery image
+#      (BOARD_USES_FULL_RECOVERY_IMAGE = true);
+#   b) We build a single image that contains boot and recovery both
+#      (BOARD_USES_RECOVERY_AS_BOOT = true).
+
+ifeq (,$(filter true, $(BOARD_USES_FULL_RECOVERY_IMAGE) $(BOARD_USES_RECOVERY_AS_BOOT)))
 # Named '.dat' so we don't attempt to use imgdiff for patching it.
 RECOVERY_RESOURCE_ZIP := $(TARGET_OUT)/etc/recovery-resource.dat
 else
-# We carry a full copy of the recovery image. recovery-resource.dat is no
-# longer needed.
 RECOVERY_RESOURCE_ZIP :=
 endif
 
@@ -929,10 +952,25 @@
     $(BOOT_SIGNER) /recovery $(1) $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_VERITY_SIGNING_KEY).pk8 $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_VERITY_SIGNING_KEY).x509.pem $(1))
   $(if $(filter true,$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_VBOOT)), \
     $(VBOOT_SIGNER) $(FUTILITY) $(1).unsigned $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_VBOOT_SIGNING_KEY).vbpubk $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_VBOOT_SIGNING_KEY).vbprivk $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_VBOOT_SIGNING_SUBKEY).vbprivk $(1).keyblock $(1))
-  $(hide) $(call assert-max-image-size,$(1),$(BOARD_RECOVERYIMAGE_PARTITION_SIZE))
+  $(if $(filter true,BOARD_USES_RECOVERY_AS_BOOT), \
+    $(hide) $(call assert-max-image-size,$(1),$(BOARD_BOOTIMAGE_PARTITION_SIZE)), \
+    $(hide) $(call assert-max-image-size,$(1),$(BOARD_RECOVERYIMAGE_PARTITION_SIZE)))
   @echo ----- Made recovery image: $(1) --------
 endef
 
+ifeq ($(BOARD_USES_RECOVERY_AS_BOOT),true)
+$(INSTALLED_BOOTIMAGE_TARGET): $(MKBOOTFS) $(MKBOOTIMG) $(MINIGZIP) \
+		$(INSTALLED_RAMDISK_TARGET) \
+		$(INTERNAL_RECOVERYIMAGE_FILES) \
+		$(recovery_initrc) $(recovery_sepolicy) $(recovery_kernel) \
+		$(INSTALLED_2NDBOOTLOADER_TARGET) \
+		$(recovery_build_prop) $(recovery_resource_deps) \
+		$(recovery_fstab) \
+		$(RECOVERY_INSTALL_OTA_KEYS)
+		$(call pretty,"Target boot image from recovery: $@")
+		$(call build-recoveryimage-target, $@)
+endif
+
 $(INSTALLED_RECOVERYIMAGE_TARGET): $(MKBOOTFS) $(MKBOOTIMG) $(MINIGZIP) \
 		$(INSTALLED_RAMDISK_TARGET) \
 		$(INSTALLED_BOOTIMAGE_TARGET) \
@@ -944,7 +982,7 @@
 		$(RECOVERY_INSTALL_OTA_KEYS)
 		$(call build-recoveryimage-target, $@)
 
-ifneq ($(BOARD_USES_FULL_RECOVERY_IMAGE),true)
+ifeq (,$(filter true, $(BOARD_USES_FULL_RECOVERY_IMAGE) $(BOARD_USES_RECOVERY_AS_BOOT)))
 $(RECOVERY_RESOURCE_ZIP): $(INSTALLED_RECOVERYIMAGE_TARGET) | $(ZIPTIME)
 	$(hide) mkdir -p $(dir $@)
 	$(hide) find $(TARGET_RECOVERY_ROOT_OUT)/res -type f | sort | zip -0qrjX $@ -@
@@ -1482,6 +1520,13 @@
 $(BUILT_TARGET_FILES_PACKAGE): $(built_ota_tools)
 endif
 
+# If we are using recovery as boot, output recovery files to BOOT/.
+ifeq ($(BOARD_USES_RECOVERY_AS_BOOT),true)
+$(BUILT_TARGET_FILES_PACKAGE): PRIVATE_RECOVERY_OUT := BOOT
+else
+$(BUILT_TARGET_FILES_PACKAGE): PRIVATE_RECOVERY_OUT := RECOVERY
+endif
+
 # Depending on the various images guarantees that the underlying
 # directories are up-to-date.
 $(BUILT_TARGET_FILES_PACKAGE): \
@@ -1500,28 +1545,28 @@
 	@echo "Package target files: $@"
 	$(hide) rm -rf $@ $(zip_root)
 	$(hide) mkdir -p $(dir $@) $(zip_root)
-ifneq ($(INSTALLED_RECOVERYIMAGE_TARGET),)
+ifneq (,$(INSTALLED_RECOVERYIMAGE_TARGET)$(filter true,$(BOARD_USES_RECOVERY_AS_BOOT)))
 	@# Components of the recovery image
-	$(hide) mkdir -p $(zip_root)/RECOVERY
+	$(hide) mkdir -p $(zip_root)/$(PRIVATE_RECOVERY_OUT)
 	$(hide) $(call package_files-copy-root, \
-		$(TARGET_RECOVERY_ROOT_OUT),$(zip_root)/RECOVERY/RAMDISK)
+		$(TARGET_RECOVERY_ROOT_OUT),$(zip_root)/$(PRIVATE_RECOVERY_OUT)/RAMDISK)
 ifdef INSTALLED_KERNEL_TARGET
-	$(hide) $(ACP) $(INSTALLED_KERNEL_TARGET) $(zip_root)/RECOVERY/kernel
+	$(hide) $(ACP) $(INSTALLED_KERNEL_TARGET) $(zip_root)/$(PRIVATE_RECOVERY_OUT)/kernel
 endif
 ifdef INSTALLED_2NDBOOTLOADER_TARGET
 	$(hide) $(ACP) \
-		$(INSTALLED_2NDBOOTLOADER_TARGET) $(zip_root)/RECOVERY/second
+		$(INSTALLED_2NDBOOTLOADER_TARGET) $(zip_root)/$(PRIVATE_RECOVERY_OUT)/second
 endif
 ifdef BOARD_KERNEL_CMDLINE
-	$(hide) echo "$(BOARD_KERNEL_CMDLINE)" > $(zip_root)/RECOVERY/cmdline
+	$(hide) echo "$(BOARD_KERNEL_CMDLINE)" > $(zip_root)/$(PRIVATE_RECOVERY_OUT)/cmdline
 endif
 ifdef BOARD_KERNEL_BASE
-	$(hide) echo "$(BOARD_KERNEL_BASE)" > $(zip_root)/RECOVERY/base
+	$(hide) echo "$(BOARD_KERNEL_BASE)" > $(zip_root)/$(PRIVATE_RECOVERY_OUT)/base
 endif
 ifdef BOARD_KERNEL_PAGESIZE
-	$(hide) echo "$(BOARD_KERNEL_PAGESIZE)" > $(zip_root)/RECOVERY/pagesize
+	$(hide) echo "$(BOARD_KERNEL_PAGESIZE)" > $(zip_root)/$(PRIVATE_RECOVERY_OUT)/pagesize
 endif
-endif
+endif # INSTALLED_RECOVERYIMAGE_TARGET defined or BOARD_USES_RECOVERY_AS_BOOT is true
 	@# Components of the boot image
 	$(hide) mkdir -p $(zip_root)/BOOT
 ifeq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE),true)
@@ -1532,6 +1577,8 @@
 	$(hide) $(call package_files-copy-root, \
 		$(TARGET_ROOT_OUT),$(zip_root)/BOOT/RAMDISK)
 endif
+	@# If we are using recovery as boot, this is already done when processing recovery.
+ifneq ($(BOARD_USES_RECOVERY_AS_BOOT),true)
 ifdef INSTALLED_KERNEL_TARGET
 	$(hide) $(ACP) $(INSTALLED_KERNEL_TARGET) $(zip_root)/BOOT/kernel
 endif
@@ -1548,6 +1595,7 @@
 ifdef BOARD_KERNEL_PAGESIZE
 	$(hide) echo "$(BOARD_KERNEL_PAGESIZE)" > $(zip_root)/BOOT/pagesize
 endif
+endif # BOARD_USES_RECOVERY_AS_BOOT
 	$(hide) $(foreach t,$(INSTALLED_RADIOIMAGE_TARGET),\
 	            mkdir -p $(zip_root)/RADIO; \
 	            $(ACP) $(t) $(zip_root)/RADIO/$(notdir $(t));)
@@ -1586,6 +1634,9 @@
 ifdef BOARD_BOOTIMAGE_PARTITION_SIZE
 	$(hide) echo "boot_size=$(BOARD_BOOTIMAGE_PARTITION_SIZE)" >> $(zip_root)/META/misc_info.txt
 endif
+ifeq ($(BOARD_USES_RECOVERY_AS_BOOT),)
+	$(hide) echo "recovery_as_boot=$(BOARD_USES_RECOVERY_AS_BOOT)" >> $(zip_root)/META/misc_info.txt
+endif
 ifeq ($(INSTALLED_RECOVERYIMAGE_TARGET),)
 	$(hide) echo "no_recovery=true" >> $(zip_root)/META/misc_info.txt
 endif
@@ -1638,6 +1689,7 @@
 	done
 	@# Include the build type in META/misc_info.txt so the server can easily differentiate production builds.
 	$(hide) echo "build_type=$(TARGET_BUILD_VARIANT)" >> $(zip_root)/META/misc_info.txt
+	$(hide) echo "ab_update=true" >> $(zip_root)/META/misc_info.txt
 ifdef OSRELEASED_DIRECTORY
 	$(hide) $(ACP) $(TARGET_OUT_ETC)/$(OSRELEASED_DIRECTORY)/product_id $(zip_root)/META/product_id.txt
 	$(hide) $(ACP) $(TARGET_OUT_ETC)/$(OSRELEASED_DIRECTORY)/product_version $(zip_root)/META/product_version.txt
@@ -1655,9 +1707,8 @@
 	$(hide) zipinfo -1 $@ | awk 'BEGIN { FS="VENDOR/" } /^VENDOR\// {print "vendor/" $$2}' | $(HOST_OUT_EXECUTABLES)/fs_config -C -D $(TARGET_OUT) -S $(SELINUX_FC) > $(zip_root)/META/vendor_filesystem_config.txt
 ifeq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE),true)
 	$(hide) zipinfo -1 $@ | awk 'BEGIN { FS="ROOT/" } /^ROOT\// {print $$2}' | $(HOST_OUT_EXECUTABLES)/fs_config -C -D $(TARGET_OUT) -S $(SELINUX_FC) > $(zip_root)/META/root_filesystem_config.txt
-else
-	$(hide) zipinfo -1 $@ | awk 'BEGIN { FS="BOOT/RAMDISK/" } /^BOOT\/RAMDISK\// {print $$2}' | $(HOST_OUT_EXECUTABLES)/fs_config -C -D $(TARGET_OUT) -S $(SELINUX_FC) > $(zip_root)/META/boot_filesystem_config.txt
 endif
+	$(hide) zipinfo -1 $@ | awk 'BEGIN { FS="BOOT/RAMDISK/" } /^BOOT\/RAMDISK\// {print $$2}' | $(HOST_OUT_EXECUTABLES)/fs_config -C -D $(TARGET_OUT) -S $(SELINUX_FC) > $(zip_root)/META/boot_filesystem_config.txt
 ifneq ($(INSTALLED_RECOVERYIMAGE_TARGET),)
 	$(hide) zipinfo -1 $@ | awk 'BEGIN { FS="RECOVERY/RAMDISK/" } /^RECOVERY\/RAMDISK\// {print $$2}' | $(HOST_OUT_EXECUTABLES)/fs_config -C -D $(TARGET_OUT) -S $(SELINUX_FC) > $(zip_root)/META/recovery_filesystem_config.txt
 endif
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index ee0cdf9..aaf51e9 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -494,8 +494,11 @@
     info_dict = OPTIONS.info_dict
 
   # With system_root_image == "true", we don't pack ramdisk into the boot image.
-  has_ramdisk = (info_dict.get("system_root_image", None) != "true" or
-                 prebuilt_name != "boot.img")
+  # Unless "recovery_as_boot" is specified, in which case we carry the ramdisk
+  # for recovery.
+  has_ramdisk = (info_dict.get("system_root_image") != "true" or
+                 prebuilt_name != "boot.img" or
+                 info_dict.get("recovery_as_boot") == "true")
 
   fs_config = "META/" + tree_subdir.lower() + "_filesystem_config.txt"
   data = _BuildBootableImage(os.path.join(unpack_dir, tree_subdir),
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index 5259ede..a76eaa9 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -1703,7 +1703,9 @@
   if OPTIONS.device_specific is not None:
     OPTIONS.device_specific = os.path.abspath(OPTIONS.device_specific)
 
-  if OPTIONS.info_dict.get("no_recovery") == "true":
+  ab_update = OPTIONS.info_dict.get("ab_update") == "true"
+
+  if OPTIONS.info_dict.get("no_recovery") == "true" and not ab_update:
     raise common.ExternalError(
         "--- target build has specified no recovery ---")
 
@@ -1725,8 +1727,9 @@
     output_zip = zipfile.ZipFile(temp_zip_file, "w",
                                  compression=zipfile.ZIP_DEFLATED)
 
+  # Non A/B OTAs rely on /cache partition to store temporary files.
   cache_size = OPTIONS.info_dict.get("cache_size", None)
-  if cache_size is None:
+  if cache_size is None and not ab_update:
     print "--- can't determine the cache partition size ---"
   OPTIONS.cache_size = cache_size
 
@@ -1736,7 +1739,11 @@
 
   # Generate a full OTA.
   elif OPTIONS.incremental_source is None:
-    WriteFullOTAPackage(input_zip, output_zip)
+    if ab_update:
+      # TODO: Pending for b/25715402.
+      pass
+    else:
+      WriteFullOTAPackage(input_zip, output_zip)
 
   # Generate an incremental OTA. It will fall back to generate a full OTA on
   # failure unless no_fallback_to_full is specified.