Disclosed are formulation and optimization protocols for delivery of therapeutically effective amounts of biologically active agents to liver, tumors, and/or other cells or tissues. Also provided are compositions and uses for cationic lipid compounds of formula (I). The invention also relates to compositions and uses for stealth lipids of formula (XI). Also provided are processes for making such compounds, compositions, and formulations, plus methods and uses of such compounds, compositions, and formulations to deliver biologically active agents to cells and/or tissues.