This chapter emphasizes recent progress in the use of baculovirus expression vectors, especially in regard to applications in agriculture and medicine, and outlines the characteristics of baculovirus expressed proteins. It covers the unique advantages of expression in insect larval systems. Baculoviruses are characterized by circular double-stranded DNA genomes that are encapsulated within rod-shaped enveloped virions. The baculovirus genome is composed of 100 to 180 kbp of double-stranded circular DNA. The expression of baculovirus genes is temporally regulated and characterized by three distinct phases: early, late, and very late. Due to the large size of the baculovirus genome, a foreign gene construct cannot be directly inserted into the viral genome. The polyhedrin promoter has several characteristics that make it ideal for driving foreign gene expression. Other baculovirus late gene promoters including those of the basic DNA binding and capsid proteins have been used to drive foreign gene expression.