A shareholder is typically an individual or entity that has an ownership stake in the corporation (a C Corporation or an S Corporation, among others). Shareholders become shareholders by putting money or property into the corporation, or by being granted stock in the corporation (which might have its own tax consequences, frequently overlooked until the piper comes calling). A shareholder can be a large corporation or an individual like you. Shareholders are charged with, among other things, electing the board of directors and approving certain corporate transactions. So ultimately shareholders call the shots. Ideally a group of shareholders would set out their relationship with each other in a Shareholders Agreement to protect themselves from a number of unforeseen events. “Stockholder” and “shareholder” typically means the same thing.