The advent of continuous human leukemia–lymphoma cell lines as a rich resource of abundant, accessible, and manipulable living cells has contributed significantly to a better understanding of the pathophysiology of hematopoietic tumors. The first leukemia–lymphoma cell lines were established in 1963 and since then large numbers of new cell lines have been described. The major advantages of continuous leukemia–lymphoma cell lines are the unlimited supply and worldwide availability of identical cell material and the infinite viable storability in liquid nitrogen. These cell lines are characterized generally by monoclonal origin and differentiation arrest, sustained proliferation in vitro under preservation of most cellular features, and by specific genetic alterations. Here some of the more promising techniques for establishing new leukemia–lymphoma cell lines and the basic principles for culturing these cells are described. Several clinical and cell culture parameters might have some influence on the success rate, e.g., choice of culture medium and culture conditions, specimen site of the primary cells, and status of the patient at the time of sample collection.