Surface free energy (SFE) is the excess energy per unit surface area. It is a quantitative thermodynamic measure of intermolecular and surface forces, thus also determining the hydrophobicity and wettability of a material. The SFE of a liquid surface is equivalent to its surface tension, which can be determined with established methods. However, the SFE of a solid surface cannot be determined directly. The SFE of micro- and nanoparticles plays a crucial role in determining dispersion and aggregation of the particles. To date, there are no easy-to-use methods for determining the SFE of particles. In this seminar, I will introduce novel methods developed in our laboratory for determining the SFE of liquids, solids, and particles. Applications in nano-bio interactions, bacterial adhesion, and applied surface thermodynamics will be discussed.