Simply visit your Zotero account profile and select a storage plan.

There would be significant costs associated with providing free file storage to the hundreds of thousands of Zotero users. The Zotero project doesn't monetize user data or otherwise profit from its users, and so there must be a means of recovering these costs.

Zotero File Storage involves more than just a pile of hard drives. The Zotero development team and the Corporation for Digital Scholarship have built an entire service architecture devoted to the needs of researchers, including the ability to move files seamlessly between group and personal libraries, and to access these files easily via the Zotero client or at zotero.org. Physically storing the files is just one component of a service that allows for real-time synchronization and distribution among multiple computers and individual and group users. Despite this complexity, Zotero File Storage pricing remains comparable to many far more basic, online backup services.

Zotero File Storage involves a customized data layer running on Zotero servers, backed by file storage hosted with Amazon's Simple Storage Service (S3).

5 TB (the limit for Amazon S3).

All payment and billing information is handled only by Google Checkout. Zotero and the Corporation for Digital Scholarship never see your credit card number, only confirmation that your payment has been processed.