You can choose between the following formats:

YAML: Best for exporting data.
Please note that importing YAML files is currently supported only in experimentally. Do not rely on it for backing up critical data.
CSV: Best for importing into spreadsheet or data analysis software
XML: Best for importing or repurposing the data

Description	Download link
YAML file containing all your actions, contexts, projects, tags and notes	<%= link_to "YAML file", :controller => 'data', :action => 'yaml_export' %>
CSV file containing all of your actions, with named contexts and projects	<%= link_to "CSV file (actions, contexts and projects)", :controller => 'data', :action => 'csv_actions' %>
CSV file containing all your notes	<%= link_to "CSV file (notes only)", :controller => 'data', :action => 'csv_notes' %>
XML file containing all your actions, contexts, projects, tags and notes	<%= link_to "XML file (actions only)", :controller => 'data', :action => 'xml_export' %>