An EWOD device includes a first substrate assembly and a second substrate assembly; wherein one of said substrate assemblies includes electrowetting electrodes, and the first substrate assembly and the second substrate assembly are spaced apart to define a channel between the substrate assemblies; and a housing for receiving the first substrate assembly and the second substrate assembly, the housing comprising an alignment feature for locating at least one of the first and second substrate assemblies within the housing. The device further includes a fixing feature for fixing the first and second substrate assemblies within the housing. The second substrate assembly is located within the housing such that the second substrate assembly is an outer component of the EWOD device. The device further may include a spacer that spaces apart the first substrate assembly from the second substrate assembly to define the channel between the first and second substrate assemblies.