Teresa Southwick is an American author of romance novels whose work has been adapted into manga. Her career as a writer began in 1994 with the publication of her novels, and she has since written numerous contemporary and historical romance titles, primarily for publishers such as Harlequin and Silhouette Books.

While Southwick is originally from California and has also lived in Texas, she is based in Las Vegas, Nevada. Her body of work includes series such as the Buy-A-Guy series, the Brothers of Bha'Khar series, and the Destiny, Texas series, among many others. Her novel In Good Company was originally published in 2006 as part of her Buy-A-Guy series. The book was recognized with a Romantic Times Reviewers' Choice Award that same year.

Southwick's significance in the context of anime and manga stems from the adaptation of her romance novels into illustrated works. The manga In Good Company is one such example. This manga is credited to Teresa Southwick as the original creator, with artwork by the manga artist Keiko Okamoto. It was published by Harlequin/SB Creative, a publisher known for adapting romance novels into the josei manga genre, which is targeted toward adult women. The story follows the original novel's plot about a woman confronting a past relationship.