  In this survey paper we present recent results obtained by Khare,
Wintenberger and the author that have led to a proof of Serre's conjecture,
such as existence of compatible families, modular upper bounds for universal
deformation rings and existence of minimal lifts, prime switching and
modularity propagation, weight reduction (via existence of conjugates) and
(iterated) killing ramification.
  The main tools used in the proof of these results are modularity lifting
theorems a la Wiles and a result of potential modularity due to R. Taylor.
