These lecture notes give an introduction to deformations of Galois representations with an eye toward the application of this theory in the proof of the Serre conjecture [29, 30] by Khare–Wintenberger. There exist several other surveys such as [18, 23, 37, 40]. We nevertheless hope that with the above scope in mind and by the arrangement and detail of the material presented we can add something useful to the existing literature. Clearly, we claim no originality in the material presented and all errors are to be blamed on the present author.