Free Book - Princeton University

There is a very good free book. This accompanies the Princeton University Bitcoin and Cryptocurrency Technologies Online Course.

"Bitcoin and Cryptocurrency Technologies" provides a comprehensive introduction to the revolutionary yet often misunderstood new technologies of digital currency.

Download the free PDF book at:
https://d28rh4a8wq0iu5.cloudfront.net/bitcointech/readings/princeton_bitcoin_book.pdf

One of the best resources...

One of the best resources I have come across is from Princeton University. There are a set of 12 video lectures on Youtube - https://www.youtube.com/channel/UCNcSSleedtfyDuhBvOQzFzQ