The patch-clamp technique, invented by Erwin Neher and Bert Sakmann in 1976, was originally designed to detect the activity of single-ion channel proteins in the cell membrane. The technique is now widely used in the field of ion channel research for many purposes, such as to monitor changes in the total membrane current, intracellular voltage or cell membrane capacitance etc. in a living cell at high time resolution. We explain the basic principle of, and protocols for, the patch-clamp technique, including maneuvers for patch-clamp amplifier operation – basic knowledge required for applications explained in the following chapters.