[1] Ralls' research interests are in the behavioral ecology, genetics, and conservation of mammals, both terrestrial and marine.

Since 1980, she has focused on conservation biology, especially the genetic problems of small captive and wild populations.

Two mammals that she has studied extensively are the sea otter and the San Joaquin kit fox.

[3] In 2017, Ralls, Ballou, and Richard Frankham published the first book on the genetic management of fragmented species populations, "Genetic Management of Fragmented Animal and Plant Populations.

"[9] In addition to her Smithsonian appointment, Ralls is a research associate at the Institute of Marine Sciences, University of California, Santa Cruz.