A great many efforts have been made to accelerate the drug discovery and development process, which is extremely time and money consuming. Recently developed molecular imaging has many significant advantages over conventional methods for examining molecular pathways and obtaining pharmacokinetic, pharmacodynamic and mechanistic information. This review briefly summarizes various molecular and cellular imaging techniques and discusses several important applications of molecular and cellular imaging in drug discovery and development, which include: (i) measurement of pharmacodynamic endpoints by imaging metabolism and proliferation, imaging angiogenic parameters, and imaging a particular pathway or downstream target; (ii) evaluation of pharmacokinetics; and (iii) imaging therapeutic gene expression with relevance to gene therapy. Molecular imaging is becoming more widely used as a non-invasive tool for drug discovery and drug screening. Further refinements in imaging techniques, optimization of imaging probes and collaborative efforts will be needed to fully realise the vast potential of molecular imaging techniques in discovering and developing new drugs.