This chapter explores the intricate interplay between transposable elements (TEs) and the immune system, emphasizing their dual role as regulators and activators within immune pathways. TEs have been co-opted to play critical roles in immune cell function and the regulation of immune-related genes, serving as cis-regulatory elements that shape transcriptional networks. Beyond these regulatory functions, the activation of endogenous TEs can profoundly impact immune responses, particularly through their ability to initiate immune signaling cascades. This process, termed viral mimicry, occurs when endogenous TE-derived nucleic acids are expressed and detected in the cytosol, triggering antiviral interferon responses. Such TE-driven immune modulation represents a promising approach for enhancing anti-cancer immunity. Furthermore, TE-derived transcripts demonstrate immunogenic potential and act as a reservoir for neoantigen generation. Overall, this chapter provides a comprehensive overview of the multifaceted roles of TEs in shaping immune responses, with a focus on their translational potential in cancer therapy.