Transposable Elements are fragments of DNA that can move themselves from one place in a genome to another, creating mutations and potentially genome instability. To control transposable elements, eukaryotic cells target them with chromatin modifications and/or DNA methylation to repress their transcription, and this regulation can be heritable (epigenetic). The Slotkin lab's long-term goal has been understand how plant cells first recognize transposable elements and trigger the cycle of chromatin modification and epigenetic silencing. We have used the transfer of foreign transposable elements from other plant species and fungi into the reference plant Arabidopsis to study the de novo initiation of epigenetic silencing, and through this process uncovered how to keep a foreign transposable element active in a plant genome. This control over transposable element activity is useful for genome engineering, as we can now control the activity, insertion site, cargo and timing of transposable elements in Arabidopsis and the major crop Soybean. Using transposable elements and a programmable nuclease such as Cas9 has provided us newfound control over transposable elements and the evolutionary processes they drive.