Antibody has become a major category of therapeutics. However, IgG, the primary molecular format of existing antibody drugs, has some major shortcomings such as undesirable pharmacokinetics, high dose requirement, and high production cost, partially due to its large molecular size. Much efforts have been made to address these issues, which usually led to antibodies or antibody fragments with smaller size. However, in most cases these changes also resulted in complete or partial deletion of fragment crystal-lizable (Fc), which is known to be crucial for a long serum half-life through binding to FcRn and antibody-mediated cell killing through binding to Fcγ receptors and complement. Single-domain antibodies (sdAbs) derived from camelid heavy-chain antibodies (HCAbs) provide an excellent building block for constructing antibodies with moderate size yet with an intact Fc. We describe in this chapter the construction, production, and purification of chimeric HCAbs (cHCAbs), that is, fusion of camelid sdAb to human Fc. The cHCAb has a molecular size approximately half that of IgG (80 kDa vs. 150 kDa). Production is achieved through a transient expression with a human embryonic kidney (HEK) expression system, which can rapidly provide hundreds of milligrams to low-gram quantities of soluble and glycosylated recombinant antibodies for early-stage drug development. ; peer reviewed: yes ; NRC Pub: yes