RNA interference (RNAi) is a post-transcriptional mechanism that uses small RNA molecules to inhibit translation or degrade messenger RNA. The functions of RNAi in fungi include transposon suppression, protection against viruses, DNA damage, transgene silencing, gene regulation as well as heterochromatin formation. Important genes essential for the function of RNAi include Argonaute, Dicer and RNA-dependent RNA polymerase (RdRP). In the plant pathogen Fusarium circinatum, very little is known about RNAi and the genes involved in this process. F. circinatum is an economically important fungus as it causes pine pitch canker on mature Pinus species and Douglas fir trees. This pathogen also causes root and collar rot in young pine seedlings. My project focuses on RNAi in F. circinatum. The first research chapter investigates RNAi-related genes in F. circinatum and closely related species. In the second research chapter, I will apply dsRNA, an RNA silencing trigger, to decrease the expression of a selected number of genes in F. circinatum.