You'll need an internet connection to access Office 365, but you don't have to stay connected to work. All Office 365 plans require internet connectivity to be installed and activated at first. Remember that if you need to access cloud-stored documents, you will need to connect to the internet to download files and work offline. Access to Office 365 cloud services such as e-mail, real-time co-authoring of documents, and conferencing will also be restricted.