Other media celebrities in the publication's alphabetical list of its top 50 include actresses Tina Fey, Angelina Jolie, Julia Louis-Dreyfus, Melissa McCarthy and Gwyneth Paltrow; singers Mariah Carey and Gwen Stefani; newswoman Katie Couric; and model Gisele Bündchen.
The magazine says it selected women who "have exhibited the strength to overcome tremendous obstacles, the insight to innovate and inspire, and the passion and courage to go against the grain to change the lives of others for the better." And they had to have at least one child under age 18.
Beyoncé, who gave birth to daughter Blue Ivy last year, was lauded for performing at President Obama's second inauguration and at Super Bowl halftime, releasing a self-produced HBO documentary as well as a new album, and scoring a multimillion-dollar Pepsi endorsement.
Lopez, who has 5-year-old twins Max and Emme, was an "American Idol" judge this year and co-chairwoman of the charitable Mobile Alliance for Maternal Action's Global Mom Relay, which works to bring medical access to mothers in the developing world. Pregnant "Fashion Star" mentor Simpson, mother of a daughter Maxwell, 1, has a $20 million fashion line.