"Zero Knowledge" cryptography refers to a powerful set of techniques and tools that allow participants in a network to prove facts about computations (knowledge of a secret number; correct execution of a function; etc.) while partially concealing information about the computations. For example, zero-knowledge cryptography might allow a user of a cryptocurrency network to deposit or withdraw currency from a vault, without revealing to the wider network the amounts that they are depositing or withdrawing.
ZK is a hot topic, and there is active work being done on ZK cryptography at all levels of the stack. Researchers are continuously working on constructing better, faster, and more general ZK protocols. Engineers are continuously working to implement these systems, and application developers are coming up with different ways to build DApps of increasing levels of complexity/usability by leveraging ZK tools.
Correspondingly, this collection contains several subtopics; some will be more interesting to math/theory-oriented readers, while others will be more interesting to engineers and builders. Each subtopic has a list of Readings, which may include articles, papers, and tutorials, and a possibly a list of Quests, which are hands-on activities you can do to cement your knowledge.