The epigenetics of COVID-19 is a rapidly expanding field that reveals how the SARS-CoV-2 virus initiates alterations in the host’s genome, influencing the susceptibility to infection, the disease severity, and long-term consequences, known as “long COVID.” In this review, we describe the mechanisms utilized by the virus to manipulate the host epigenome, suppressing antiviral responses and creating a favorable environment for viral replication. We also highlight virus-induced epigenetic changes across diverse cell populations that contribute to COVID-19 pathogenesis. Notably, the virus reprograms hematopoietic stem and progenitor cells, leading to long-lasting alterations in innate immunity, a phenomenon known as “trained immunity.” These epigenetic modifications are maintained in differentiated daughter cells and may explain the persistent inflammation and other symptoms of long COVID. Furthermore, we discuss emerging epigenetic biomarkers of disease severity, including methylation signatures in genes such as AIM2, HLA-C, and PARP9, as well as dysregulated miRNA profiles. Understanding this complex interplay between the virus and the host’s epigenetic landscape is crucial for developing new therapeutic approaches that target specific epigenetic modifications to suppress pathological processes and improve clinical outcomes for COVID-19 patients.