This chapter delves into the concepts of mood and modal verbs in English, exploring the nuances of modality and how modal auxiliaries function within the language system. It distinguishes between tense auxiliaries and modal auxiliaries, highlighting their unique characteristics regarding tense and function. The chapter then examines specific modal pairs and groups, including can vs. could, will vs. would, and could vs. would, clarifying their contextual usage for expressing ability, possibility, politeness, suggestions, requests, offers, and conditional situations. It also covers the auxiliaries must, shall, and should, detailing their roles in conveying necessity, obligation, determination, intention, willingness, and probability. Finally, it introduces may and might.