This is about installing Emacs into an Android device. See GoogleAndroid for tips about using Emacs to develop Android applications.

Ways to run Emacs on Android devices

Native port (installable Android application)

A native Emacs on Android, without requiring root or special setup, can be installed in a chroot environment such as provided by UserLand which can even give an optional desktop environment.

With UserLand, you can install a variety of different distributions. Here are some of the commands to install emacs on some of them:

Another solution is Termux. There, just Debian is supported.

In Alpine (recommended)

apk update && apk add emacs

In Arch Linux

pacman -Syu && pacman -S emacs

In Debian/Ubuntu

apt update && apt install emacs

Run Linux inside a jail

GNU/Linux in a chroot jail (requires root)

For a Linux and Emacs environment in a chrooted loopback filesystem on a rooted tablet, see Running Emacs on an Android tablet. Android apps such as ConnectBot shell client and Hacker’s Keyboard (including Ctrl, etc. keys) can be used with Emacs in this way.

Don't run Emacs, use a SSH client to connect to a server which runs Emacs

This is by far the easiest and fastest way. It does not require uninstalling Android, and Emacs will run at normal speed. You could also use VNC if you need graphics.