Liquid-phase transmission electron microscopy (LPTEM) is a powerful technique for in situ visualization and direct characterization of dynamic matter in the liquid state with an unprecedented spatial (nanometer) and temporal (millisecond) resolution. By encapsulating a small amount of liquid specimen in either commercially available micro-fabricated cells with electron transparent silicon nitride (SiNx) windows or non-commercial graphene cells, researchers have observed the dynamics of nanostructured materials using transmission electron microscopes. LPTEM has recently led to several advancements in various fields, including understanding the morphological transformation and dynamics of nanocrystals, catalytic nanomaterials, chemical and biological soft materials, batteries, and emulsions. Despite this advancement, there are challenges in understanding, controlling, and mediating the effect of the microscope's electron beam on the specimen. This Methods Collection presents various methods developed in the past decade, from both experimental and computational aspects, to build LPTEM as a robust quantitate method for studying the dynamics of materials in the liquid state at the nanoscale.