Part-of-Speech (POS) tagging is a fundamental aspect of text processing in NLP. This chapter explores its significance in relation to both NLP and Natural Language Understanding (NLU). It covers various types and algorithms for POS tagging, including rule-based POS Tagging, stochastic POS Tagging, and hybrid POS tagging, with a focus on Brill’s Tagger and associated evaluation methods. Additionally, this chapter lays the groundwork for Workshop #3: Part-of-Speech Tagging using Natural Language Toolkit (NLTK), presented in Chap. 13 .