Generalizations of small cancellation theory
Conjugacy growth functions
Quasi-cocycles, bounded cohomology and stable commutator length
Asymptotic cones
Transitivity degrees and highly transitive actions
The elementary/universal theory of groups and equations in groups
Limit groups and Makanin-Razborov diagrams
Descriptive set theory and the space of marked groups
My papers can be found on the arXiv