Yes. You can import directly from Outlook or indirectly via a CSV file. Excel spreadsheets can be saved as .csv files and most popular desktop software packages including ACT!, Quickbooks, and other contact management systems also provide easy export to a .csv file format. 

GEM also has an 'Extract Wizard' that will extract data from any ODBC compliant data source and an 'Import Wizard' that will import data from multiple data sources into GEM.