Pamela Lillian Isley, aka Poison Ivy, is a Gotham City botanist obsessed with plants, ecological extinction, and environmentalism. The dangerous experiments that transformed Pamela into Poison Ivy placed a deliberate overdose of plant and animal-based toxins into her bloodstream that makes her touch deadly while also allowing her to boost her immunity to virtually all pathogens. She uses plant toxins and pheromones to aid in her criminal activities, which are usually aimed at protecting endangered species and the natural environment. 

Although she is generally a supervillain, she and Batman have worked together in the past. There has always been sexual tension between Poison Ivy and Batman, who sometimes team up to pursue a common goal. She has repeatedly said that she is in love with Batman and has, time after time, chosen to not kill him. There are storylines where Batman is portrayed as returning her affections. 

Poison Ivy and Harley Quinn frequently team up to commit crimes together. They have a close friendship, and Ivy attempts to help Harley Quinn end her unhealthy relationship with The Joker. 

In June 2015, Harley Quinn writers Jimmy Palmiotti and Amanda Connor confirmed that Poison Ivy is bi and that she and Harley are in a romantic relationship.

The 2019 animated series Harley Quinn explores Poison Ivy and Harley Quinn's romance much more than in previous versions.