Mass spectrometry involves the measurement of the mass-to-charge ratio of ions. It has become an essential analytical tool in biological research and can be used to characterize a wide variety of biomolecules such as sugars, proteins, and oligonucleotides. In this review, a brief history of mass spectrometry is discussed, and the basic principles of the technology are introduced. A summary of some current applications is provided, as are examples of recently published research. The current methods used to identify, quantify, and characterize proteins and peptides are then reviewed. The range of applications of mass spectrometry is considerable and only promises to grow as the technology continues to improve.