Thoracic electrical bioimpedance (TEB) is a harmless, noninvasive, user-friendly technology with wide patient acceptance. Stroke volume (SV) determination is important because it helps to define oxygen transport. Measurement of SV by TEB is rooted in concrete, basic electrical theory, as well as in theoretical models of electrical behavior of the human thorax and great thoracic vessels. This article is concerned with basic electrical theory as applied to TEB, signal acquisition, and the origin of the thoracic cardiogenic impedance pulse (delta Z). The appendix of the chapter features a more extensive overview of alternating current theory as applied to electrical bioimpedance.