Upwork is one of the largest freelance marketplaces with over 14 million users from 180 countries. Freelancers on Upwork provide a wide range of services - technical, creative, administrative, marketing and writing to name a few. It was created in 2015, from the merging of Elance (1999) and oDesk (2003), two of the largest online freelance platform at the time, and remain a major and dominant player.
Upwork provides flexible billing and project management tools and is one of the easiest platforms to get started on. Building a reputable profile on Upwork can take some time, and usually requires starting with lower rates, but if you have the time and are good at what you do Upwork can serve as a stable and long-term source of work.