Major League Baseball (MLB) | 409,280 followers on LinkedIn. Step Up to the Plate | Major League Baseball (MLB) is the most historic professional sports league in the United States and consists of 30 member clubs in the U.S. and Canada, representing the highest level of professional baseball. Led by Commissioner Robert D. Manfred, Jr., MLB remains committed to making an impact in the communities of the U.S., Canada and throughout the world, perpetuating the sport's larger role in society and permeating every facet of baseball's business, marketing, community relations and social responsibility endeavors.