Pseudoviridae belongs to the order Ortervirales, class Revtraviricetes. It has three genera, namely, Pseudovirus, Hemivirus, and Sirevirus, and members can be found in association with many plants, animals, and fungi and share common features in terms of evolutionary history, structure, and function. They multiply their genomes through reverse transcription. The term Pseudovirus has evolved from Greek language with meaning of “false,” to imply an evolutionary relationship to viruses having extracellular virions, while the name Sirevirus which was created in 2004 (Mayo 2005) has derived from the species name glycine max SIRE1 virus. The genus Hemivirus is not discussed in this chapter as none of its eight species are isolated from plants. Laying cornerstones to the taxonomy of Pseudoviridae goes back to the 1980s and 1990s. For instance, analysis of Ty1/Copia group retrotransposon from more than 50 species of plants by Flavell et al. (1992) revealed that having a varied divergence in terms of sequence data between pairs of sequences, implying that sequence divergence during vertical transmission of Ty1/Copia elements within plant lineages as a major factor in the evolutionary process of Ty1/Copia group members associated with higher plants. Moreover, it was suggested that horizontal transmission also has a role in this process. With time, when adding more sequence information and more related studies the information bases were revised. A transposition history of about 70,000 years could be suggestive for soybean genome that consists 1000 SIRE1 insertions that has gone through a very recent and strong amplification (Laten et al. 2003). Recently, the role of retrotransposons in terms of phenotyping and genome and gene evolution has been suggested (Sahin et al. 2020).