This chapter reviews advances in the use of entomopathogenic oomycetes as biopesticides in suppressing crop insect pests. It begins by discussing how oomycetes have evolved from invertebrate pathogens to plant pathogens, what they are commonly known as today. The chapter also provides a case study on Lagenidium giganteum as a biocontrol agent against insects. The chapter moves on to review how the mode of infection can be established by entomopathogenic oomycetes, and how oomycetes can be used as sources of novel biopesticidal metabolites. It concludes by providing potential sources for further information and directs researchers to key conferences in the field.