This textbook covers essentials of in situ and auxiliary operations necessary to operate a bioreactor where living cells are utilized as biocatalysts. Particular attention is given to the dynamic behavior of fluids within bioreactors and support equipment, thus offering a comprehensive treatment of fluid flow, pumping, flow manipulation and metering, and mixing-covering both Newtonian and non-Newtonian systems, as well as heterogeneous flow around gaseous bubbles and solid particles.A pragmatic and systematic approach is provided to all such topics, from the point of view of a biological engineer - illustrated by selected and carefully solved problems, proposed at the end of each section. Mathematical derivations are put forward that are easy to follow step-by-step - even by students holding only elementary mathematical and biochemical backgrounds; and are developed at a pace suitable for self-learning. Furthermore, the functional forms and meanings of the expressions produced are explored, and the final germane formulae are duly highlighted and graphically interpreted in dimensionless form - to facilitate the perception of major trends and asymptotic patterns. Therefore, this textbook offers a valuable resource for both instructors and undergraduate/graduate students - as an aid to grasp and relate basic physicochemical concepts underlying the actual operation of bioreactors, rather than conveying mere descriptions and empirical correlations.This textbook and the companion volumes "Fundamentals of Biocatalysts: Cell Structure and Function", "Operation Fundamentals in Bioreactor Engineering - Medium Handling" and "Modelling Fundamentals in Bioreactor Engineering" fill the gap between qualitative approaches focused on biochemistry, on the one hand; and technological approaches resorting to correlations that hardly convey a fundamental understanding of first principles, on the other.