I would start by opening the .csv file using excel and modify the column headers so they match the same fields as used in Thunderbird and save the file. For example: In Thunderbird, it has separate First Name and Last name fields. This link will tell you the names of the column headers/fields. * http://kb.mozillazine.org/Import_address_list_from_text_file How to import: In 'Address Book' Tools > Import select 'Address books' and click on 'Next Select: 'Text file' and click on Next an explorer window opens. select the folder where the .csv file is stored. At the bottom, there should be drop down option to select type of file. eg: LDIF, you need to select either the 'comma separated .csv' or 'all files' option to reveal all the .csv files. Select the .csv file you want to use and click on 'Open'. You then will be asked to map all the fields to match the appropriate thunderbird fields - useful if you have already modified the .csv file. then click on OK see image: