An ICS file is a File format for iCalendar. It can be recognized by the extension .ics . The file format allows you to Calendar entries in your calendar too import , to export and to send to other users as well as to publish entries and to release . The format is an international standard, which is why many digital calendars, such as Microsoft Outlook is software with which emails can be sent and received and appointments, notes, contacts and tasks can be managed. Official Microsoft Outlook website and Google Calendar, can handle the files and open and process the ICS files. Even converting to other popular formats is quick and easy. An ICS file can be used in all operating systems.