Treballs Finals de Grau de Matemàtiques, Facultat de Matemàtiques, Universitat de Barcelona, Any: 2015, Director: Vicenç Navarro AznarEven though the title of this composition you are reading is Gauge fields, this is just one of the many concepts that appear throughout the work. Moreover, despite the fact that this is rather a physical term (the actual mathematical name would be connections on principal G-bundles), the contents in this exposition are mathematical. As a student of both mathematics and physics, I wanted to choose a topic that could be covered in both aspects, a subject which could be interpreted physically but which had a mathematical background. This composition intends to contain the mathematical background to develop the so-called gauge theories used in modern physics such as quantum physics, particularly quantum field theory (QFT), for example quantum electrodynamics (QED) or quantum chromodynamics (QCD). However, as stated, this contains no physical conclusions, but only mathematical, with maybe some references to their physical applications. Thus, the motivation was a combination of my interest on physics (which may explain the outline and selection of topics) but also my fascination for differential geometry and topology.