OCaml is an interesting functional language. There are lots learning materials on the Internet. I compile a list of resources for OCaml learning and reference.
Recommended OCaml learning and reference material
The book from Jason Hickey and the User’s Manual from INRIA are the best material I know to learn OCaml.
A very good tutorial by Jason Hickey: http://www.cs.caltech.edu/courses/cs134/cs134b/book.pdf
The OCaml system release 3.12 Documentation and user’s manual: http://caml.inria.fr/pub/docs/manual-ocaml/
OCaml Style Guides
Other OCaml learning materials
OCaml Homepage: http://caml.inria.fr/
Introduction to OCaml on Wikipedia: http://en.wikipedia.org/wiki/OCaml
Introducing OCaml: http://www.ffconsultancy.com/products/ocaml_journal/free/introduction.html
The Harvard CS51 course which is introduced with OCaml.
A Concise Introduction to Objective Caml by David Matuszek: http://www.csc.villanova.edu/~dmatusze/resources/ocaml/ocaml.html
A good “why OCaml”: http://www.cs.ubc.ca/~murphyk/Software/Ocaml/why_ocaml.html
Blogs on OCaml from Jane Street, “where functional programming meets the real world”: http://ocaml.janestreet.com/
A very very good introduction to OCaml:
Some claim that OCaml sucks: http://sds.podval.org/ocaml-sucks.html