This licentiate thesis addresses design and development problems that arise when service providers, and service end-users face the variety of computing devices available on the market. The devices are designed for many types of use in various situations and settings, which means that they have different capabilities in terms of presentation, interaction, memory, etc. Service providers often handle these differences by creating a new version for each device. This creates a lot of development and maintenance work, and often leads to restrictions on the set of devices that services are developed for. For service end-users, this means that it can be difficult to combine devices that fit the intended usage context and services that provide the needed content. New development methods that target multiple devices from the start are needed. The differences between devices call for services that can adapt to various devices, and present themselves with device specific user interfaces. We propose a way of developing device independent services by using interaction acts to describe user-service interaction. Devices would interpret the interaction acts and generate user interfaces according to their own specific capabilities. Additional presentation information can be encoded in customization forms, to further control how the user interface would be generated. Different devices would generate different user interfaces from the same interaction acts, and a device could generate different user interfaces from the same interaction acts combined with different customization forms. In this thesis, the interaction act and customization form concepts are described in detail. A system prototype for handling them and two sample services have been implemented. Preliminary evaluations indicate that interaction acts and customization forms constitute a feasible approach for developing services with multiple user interfaces. The thesis concludes with a discussion of the problems arising when evaluating this kind of systems, and some conclusions on how to continue the evaluation process.