An Office Action is a communication from the USPTO, normally from the Trademark Examiner assigned to your application. It can address a wide variety of matters related to an application. These range from minor errors to a problem serious enough to prevent registration of the trademark. The appropriate response to an Office Action will vary depending on the nature of the Office Action and all the facts and circumstances in your case. Because the failure to timely respond to an Office Action can result in a determination that you have abandoned the application (and therefore denial of registration), it is important to take it seriously and respond to it promptly, carefully, and intelligently. If you have not engaged the services of a competent attorney to file and prosecute an application for registration already, it can be a very good idea to retain one when you receive an Office Action.