Parasites of the phylum Apicomplexa are responsible for devastating diseases in humans and livestock worldwide. Of particular importance to human health are Plasmodium species, which cause malaria that claims over 500,000 lives annually; Toxoplasma gondii, which infects roughly one-third of the global population and can result in pregnancy complications and acute illness in immunocompromised individuals; and Cryptosporidium species, which cause severe waterborne diarrheal illness. Apicomplexan parasites are obligate intracellular parasites, meaning they must invade cells of their host organism in order to replicate and survive. Due to the importance of host cell invasion in the parasite lifecycle, the extracellular invasive forms of these parasites have been under intense investigation for decades to ultimately target with therapeutics. Once the intracellular parasites are fully developed, they egress from their host cell and navigate the extracellular environment using a unique mechanism of motility known as gliding. At its core, gliding motility relies on an actomyosin motor in complex with a variety of other structural proteins, together called the glideosome. Once the extracellular parasite identifies a suitable host cell, it will create a pore in the host cell membrane through which the parasite secretes contents of specialized organelles called rhoptries, following which the parasite will anchor into the host cell membrane and engage the glideosome to penetrate the host cell and surround itself in a vacuole composed of host cell membrane. Together, motility and invasion are quick processes that require various, highly coordinated molecular events, a lot of which are still not well understood. Here, I utilized cryo-electron tomography to image Plasmodium falciparum, Toxoplasma gondii, and Cryptosporidium parvum at the nanometer scale to characterize large macromolecular complexes that are crucial for parasite motility and host cell invasion. In C. parvum and T. gondii, I discovered several structures and complexes that are involved in the biogenesis and translocation of actin filaments that are required for parasite motility. In P. falciparum, I discovered a macromolecular complex that docks the rhoptries to the site of exocytosis, as well as several configurations of the rhoptry secretion system that hint at their priming prior to secretion into the host cell. Together, this work provides a comprehensive structural understanding of the regulation of gliding and rhoptry secretion in apicomplexan parasites.