Most of blockchains do not scale well, i.e., they cannot handle quickly large amounts of transactions. One of the remedies for this problem are the so-called off-chain  (or: Layer 2) protocols where a massive bulk of transactions is kept outside of the main blockchain. In many cases such solutions dramatically improve blockchain scalability. In this talk I will give a brief introduction to Plasma, which is one of very promising off-chain protocol proposals introduced in 2017 by Poon and Buterin, and subsequently generalized to several different variants (in particular: Plasma Cash and Plasma MVP).