Over 35 years since it was established to make recombinant proteins, the baculovirus expression vector system continues to develop and improve. Early systems for recombinant virus selection were laborious, but better methods were rapidly devised that enabled non-virologists to use baculovirus vectors successfully in a wide range of applications. These applications include multiple gene expression for complex molecules, production of adeno-associated virus-like particles for gene therapy, the use of baculovirus budded virus for the same purpose, numerous potential human and animal vaccines, and for other therapeutic proteins. A number of products for human and veterinary use are now on the market, which attests to the utility of the systems. Despite these successes, baculovirus vectors essentially remain in a relatively primitive state of development. Many proteins, particularly membrane-bound or secreted products, continue to be difficult to produce. Various research groups are working to identify potential areas of improvement, which if combined into an ideal vector might offer considerable advances to the system. This chapter will review some of the most recent reports and highlight those that might have generic application for recombinant protein synthesis in insect cells. We also summarize parallel developments in host cells used for baculovirus expression and how culture conditions can influence protein production.