Diving into Clojure

So you want to start with Clojure, good. This will help you getting your environment up and running and point you to things that can easily get you started.

Installing Clojure

Installing Clojure is as easy as getting Leiningen up and running, this should be easy on most operating systems because package managers like Homebrew on OS X or your typical APT repos on $whatever already have it. So run brew install leiningen or the equivalent for your OS - also make sure you have a version >= 2.0

You also (obviously) need the JDK/JRE installed.

After this you open your favourite terminal and run lein repl which downloads Clojure and opens a REPL for you to experiment with. Quit this with (quit)

Editing Clojure

Clojure is a dialect of Lisp and, as such, very well suited for structural editing using a tool like Paredit in Emacs. In fact, Emacs is also the editor I recommend above all others, if you already use it make sure you have cider, rainbow-delimiters and paredit installed and running - take some time to get familiar with Paredit if you aren't already!

If you're new to Emacs and want to focus on Clojure you might want to look at Emacs for Clojure which installs an easy default configuration for Clojure programming.

I'm not a Vim user myself so I don't know too much about the ecosystem there, but this article lists a lot of the existing things.

If you're an IntelliJ user there's the new and experimental Cursive Clojure.

If you're a Sublime user: I honestly don't know, find out and send a pull request!

Lisp?!

To understand the concepts of Lisp please read The Nature of Lisp. Maybe don't dive into it right away but save it for later and go through it, it'll open your eyes as to why "people put up with all the parantheses in Lisp" and other such things. You will learn to love it!

Clojure environment basics

Leiningen is Clojure's dependency manager that downloads libraries for you to use from Maven repositories. If you come from the Java world, building Clojure with Maven is possible but I'm the wrong person to ask about that :-)

It also organizes your projects and creates them according to templates, there are a few important ones for learning.

default: Used by default if you specify nothing else. Creates an empty, simply structured project for library development.
app: This is a simply structured Clojure project that compiles to an executable jar file.
experiment: This is a pretty cool recent template which just gives you a single source file and a project file to quickly experiment with things. I recommend using this while learning.
compojure-app: A simple web application template based on Compojure/Ring. (More about this later)

You can now create an empty project using lein new experiment my-thing, where "my-thing" is the name of the project.

Have a look at the project.clj file to understand its structure! This is also where you add dependencies which are then automatically downloaded by Leiningen.

Learning resources

Before doing anything else, do some very basic experimentation with Try Clojure.

Koans

Koans are a way of learning a programming language through a short puzzle with a gap, you think about the code and fill in what's required until the tests pass.

If you like this style of learning I recommend that you get the Clojure Koans and work through them.

If you still want to continue in this style register on 4Clojure and start doing some of the more advanced "Koans" there.

If you want some feedback from real people on your code, register on exercism.io and work through some of their practice problems in Clojure.

Books

Programming Clojure, 2nd Edition by Stuart Halloway and Aaron Bedra. Very detailed and good book!
Clojure Programming, by Chas Emerick, Christophe Grande and Brian Carper does a good job of starting for the basics and covering a lot of practical ground.
Web Development with Clojure which does not presume Clojure experience and leads you through several short web development projects, very handy! (This book is in beta :-))

Other resources

There are lots of interesting things about Clojure on the internet, this includes talks, cool libraries and interesting tutorials. I'll try to collect the best here.

Talks

Rich Hickey (the creator of Clojure) gave one talk that I think everybody must see, not just Clojure developers, every developer: Are We There Yet?
Chris Ford's Functional Composition is a great talk about the functional nature of music (and also, a bit, about Clojure).

Cool projects

ClojureScript - Never write Javascript again! Clojure to JS compiler.
If you come from a statically typed language and are already missing your types, don't fret and look at core.typed. Ambrose, the guy who made core.typed, also appeared on the Relevance (now Cognitect) podcast and explained core.typed.
Pedestal is a cool framework for client/server web applications, made by Cognitect (formerly Relevance)
Overtone is a programmable music library which is also the one featured in Chris Ford's talk linked above. Fun to play with!
clojure-style-guide - A community coding style guide

Libraries you should know

For all JSON needs, Cheshire
Ring and Compojure, the basics of almost all Clojure web stacks
Luminus or lib-noir, both collections of useful libraries on top of Compojure and Ring
Korma, a Clojure DSL for generating SQL queries
more to come ...

Clojure podcasts

ThinkRelevance, the Relevance (now Cognitect) podcast. I think they're renaming it to Cognicast. This one is very good and has featured many interesting people!
Mostly λazy, a more informal Clojure podcast

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tazjin / clojure-basics