This review covers different key aspects of particle contacts within dense suspensions. After an introduction that motivates the necessity to account for direct surface contacts to describe the mechanical response of wet systems, we provide a general framework for contact mechanics and friction at the microscale. We then describe how friction is measured at the macroscale to introduce different methodologies developed to translate these measurements to the micro/nanoscale corresponding to interparticle contacts. The last part of the review gives a brief overview of different strategies used to modify friction and adhesion between particles. Each of the sections is accompanied by a critical discussion on perspectives and challenges for the future.