Mandel was an IBM employee from 1982 – 1993. As a member of IBM’s prestigious Common User Access (CUA) user interface architecture group, Mandel conducted research on Graphical User Interfaces (GUIs) and Object-Oriented User Interfaces (OOUIs), prototyped the IBM OS/2 operating systems interface, and wrote the landmark book, Object-Oriented Interface Design: IBM Common User Access Guidelines. Mandel also consulted with IBM on numerous projects in the past 10 years.

Long-term user experience consultant for PayPal, one of the most visited websites in the world. Mandel prototypes and designs PayPal's next generation web and mobile user experiences for consumers and merchants.

Dr. Mandel is a long-term user experience research consultant for Pearson Education, the world’s largest education company. Conducting lab and remote user testing of desktop and mobile products with teachers, students and parents. He has designed a new usability lab for Pearson in Phoenix, Arizona.

Theo Mandel was the user experience architect ton one of UnitedHealthcare’s largest internal projects for patient case management.

The multi-million dollar case management system replaced existing legacy clinical applications with a new technology framework, enhanced functionality and a world-class user interface. Mandel worked closely with nurse practitioners and case managers to understand their working environment in patient homes, nursing facilities and hospitals. He worked with business analysts and development teams to define business and technology goals. Mandel also conducted usability evaluations in the field during product beta testing.

Theo Mandel conducted heuristic evaluations of Merck’s hospital-based healthcare transition program, helping patients discharged from the hospital maintain their health and organize their post-hospital care.

Mandel conducted user research, prototyped and provided design recommendations for multiple medical assay devices. This included recommendations for software user interfaces, with the intent to eliminate user errors without requiring any additional training.

Mandel created prototypes, designed product interfaces, and conducted usability evaluations for international private banking applications. Worked with bank customers, executives, and account managers to design usable customer experiences. Lloyds TSB is a world-renowned international financial institution.

Mandel developed a Web-based Intranet user interface design guide for the fourth largest retailer in the United States. After completion, the design guide was one of the TOP 5 visited sites on the company’s Intranet and became the de facto standard for all Web development in the company.

In this project, Dr. Mandel created a “Top Ten” Intranet user interface issues document after conducting focus groups and gathering requirements. He developed the design guide as a Web site on the company’s Intranet. The guide was evaluated in a formal usability lab, using designers and developers as test participants. The guide contained libraries of Web page layouts, frames, graphic buttons and icons, and forms templates to be used across the corporation. Finally, Mandel worked with Target IT to define plans, promotions, and strategies to encourage Intranet developers to use the design guide and to participate in usability evaluations of their sites.

Mandel consulted with Swiss Bank Corporaction (SBC), which was bought by UBS. Mandel designed desktop and kiosk interfaces and conducted usability testing with bank customers in Basel, Switzerland.