diff --git a/Makefile b/Makefile
index b12d422e..a1b28674 100644
--- a/Makefile
+++ b/Makefile
@@ -36,6 +36,11 @@
 #                                     cleaned, built and booted in QEMU: the
 #                                     acceptance boot (.claude/CLAUDE.md)
 #   make boards                       list boards and whether they can be built
+#   make ARCH=<arch> init             install everything needed to build <arch>,
+#                                     boot it in QEMU and build the documents
+#                                     (Debian/Ubuntu, apt-get; sudo if not root).
+#                                     ARCH=amd64,aarch64,riscv64 sets up all
+#                                     three, for the full acceptance
 #   make <other goal>                 goes to v3/Makefile (make help-hosted)
 # ==============================================================================
 
@@ -63,7 +68,7 @@ SUBMAKE := $(MAKE) --no-print-directory
 
 .DEFAULT_GOAL := all
 .PHONY: all boot_image boot_images write_stick docs clean clean-docs kernel boards help help-hosted sbom sbom-board \
-        qemu qemu-esp qemu-gdb
+        qemu qemu-esp qemu-gdb init
 
 # ARCH given on the command line and no TARGET: `clean` is the kernel's for that
 # ISA, as `qemu` always is (make ARCH=<arch> clean qemu).
@@ -232,6 +237,37 @@ write_stick:
 	@[ -n "$(DEVICE)" ] || { echo "Usage: make write_stick DEVICE=/dev/sdX   (lsblk lists the disks)"; exit 1; }
 	@bash scripts/write_stick.sh build/boards/pc/lithos-pc.img $(DEVICE)
 
+# init -- the packages this tree needs, for one ISA or several (ARCH=amd64,aarch64,riscv64).
+# Common: the build, the disk images (scripts/mkdiskimage.sh; sfdisk is in fdisk), git-lfs for
+# the logs and DoE CSVs (.gitattributes), and the documents: the book (docs/book/Makefile's own
+# list) and the formal volumes and API reference (docs/formal/Makefile: pdflatex, doxygen, dot).
+# Per ISA: its QEMU, its UEFI firmware (kernel/Makefile's paths) and its compiler (kernel/Makefile
+# TOOLCHAIN; aarch64's loader is clang + lld-link). Not installed: syft, which make sbom and
+# boot_image need -- it is not packaged; see the message make sbom prints.
+INIT_COMMON  := build-essential make git git-lfs python3 xorriso mtools gdisk dosfstools fdisk \
+                pandoc latexmk texlive-xetex texlive-latex-base texlive-latex-recommended \
+                texlive-latex-extra texlive-pictures texlive-fonts-recommended lmodern \
+                fonts-dejavu fonts-dejavu-extra doxygen graphviz
+INIT_amd64   := qemu-system-x86 ovmf
+INIT_aarch64 := qemu-system-arm qemu-efi-aarch64 gcc-aarch64-linux-gnu binutils-aarch64-linux-gnu clang lld
+INIT_riscv64 := qemu-system-misc qemu-efi-riscv64 gcc-riscv64-linux-gnu binutils-riscv64-linux-gnu
+comma        := ,
+INIT_ARCHES  := $(subst $(comma),$(space),$(ARCH))
+INIT_BAD     := $(filter-out amd64 aarch64 riscv64,$(INIT_ARCHES))
+SUDO         := $(if $(filter 0,$(shell id -u)),,sudo)
+
+init:
+	@[ -n "$(INIT_ARCHES)" ] && [ -z "$(INIT_BAD)" ] || { \
+	    echo "Usage: make ARCH=<amd64|aarch64|riscv64>[,...] init   (e.g. ARCH=amd64,aarch64,riscv64)"; exit 1; }
+	@command -v apt-get >/dev/null 2>&1 || { \
+	    echo "init: needs apt-get (Debian/Ubuntu). The packages are listed in the Makefile, at init."; exit 1; }
+	$(SUDO) env DEBIAN_FRONTEND=noninteractive apt-get update -qq
+	$(SUDO) env DEBIAN_FRONTEND=noninteractive apt-get install -y -qq \
+	    $(INIT_COMMON) $(foreach a,$(INIT_ARCHES),$(INIT_$(a)))
+	git lfs install --local
+	@echo ""
+	@echo "Ready for $(INIT_ARCHES): make ARCH=<arch> clean qemu, make -C v4 test, make docs"
+
 help:
 	@sed -n '/^# TARGET is/,/^# =====/p' Makefile | sed '$$d; s/^# \{0,1\}//'