Chemists are constantly striving for techniques that add dimensions of orthogonality with increased throughput and sample complexity. Ion mobility spectrometry (IM) is a gasphase separation method that adds new dimensions to mass spectrometry (MS). IM separates gas-phase ions based on their collision cross-section and can be coupled with timeof- flight (TOF) mass spectrometry to yield a powerful tool used in the identification and characterization of proteins and peptides.A fundamental introduction to IM is presented with a focus on resolution, sensitivity, and orthogonality coupled with TOF-MS.