Comment by tomgag

I see a lot of comments recommending TrueCrypt/VeraCrypt here, which is fine, but did you know there is something even more interesting? ;)

Shufflecake ( https://shufflecake.net/ ) is a "spiritual successor" to TrueCrypt/VeraCrypt but vastly improved: works at the block device level, supports any filesystem of choice, can manage many nested layers of secrecy concurrently in read/write, comes with a formal proof of security, and is blazing fast (so much, in fact, that exceeds performances of LUKS/dm-crypt/VeraCrypt in many scenarios, including SSD use).

Disclaimer: it is still a proof of concept, only runs on Linux, has no security audit yet. But there is a prototype for the "Holy Grail" of plausible deniability on the near future roadmap: a fully hidden Linux OS (boots a different Linux distro or Qubes container set depending on the password inserted at boot). Stay tuned!