This chapter will focus on “small” molecule therapeutics that demonstrate useful immunosuppressant activity including established classes such as calcineurin inhibitors (cyclosporin A and tacrolimus),
mTOR
(
m
ammalian
t
arget
o
f
r
apamycin
) agents (sirolimus, everolimus), and antiproliferative/antimetabolite agents (azathioprine, mycophenolic acid derivatives). This chapter will also introduce some agents with newer pharmacology mechanisms such as sphingosine receptor modulation (FTY720), inhibition of JAK3 (CP‐690,550), and inhibition of PKC θ (AEB071). Other agents useful in organ transplantation including glucocorticoids (such as prednisone and dexamethasone), nitrogen mustards (such as cyclophosphamide), and biologic agents (such as muromonab‐CD3, basiliximab, and daclizumab) are discussed elsewhere.