By law, a corporation must designate a registered agent (also called an agent for service of process) in each state where the company has business activity deemed by the state to require the company to qualify or register with the state (often called Foreign Qualification).
The registered agent is authorized by the company to receive tax and other government notices and also any service of process in the event the company is sued, which the registered agent then forwards to the company. In addition to this basic service, registered agent services often also offer a premium service to assist a company with making its required annual report filings and franchise tax payments. Note that a registered agent does not provide general mail forwarding service -- for that, many startups use Virtual Post Mail or similar services.
For startups that incorporated using Clerky, the registered agent is one of the following:
To determine your corporation's current registered agent in a particular state, use the business entity search on the Secretary of State web site.