In the main part of this talk I will discuss the explicit realization of SU(5) GUT models in Type IIB orientifold
compactifications with intersecting D7-branes. This will include a discussion of del Pezzo transitions in Calabi-Yau threefolds which will support the GUT brane. Then I will discuss some of the tools and challenges for constructing GUT models in F-theory on compact Calabi-Yau fourfolds.