An electrowetting on dielectric (EWOD) device comprising: a first substrate assembly and a second substrate assembly respectively defining an inner surface and an opposing outer surface, wherein the first and second substrate assemblies have opposing inner surfaces; wherein the opposing inner surfaces of the first substrate assembly and the second substrate assembly are spaced apart to define a channel between the opposing inner surfaces of the first and second substrate assemblies, and wherein one of the first or second substrate assemblies (82,84) includes electrowetting electrodes for controlling movement of a droplet of fluid in the channel of the EWOD device; a housing (92, 110) for receiving at least one of the first substrate assembly and the second substrate assembly (82,84), the housing comprising an alignment feature for locating at least one of the first and second substrate assemblies within the housing; and a fixing feature for fixing the at least one of the first and second substrate assemblies within the housing; wherein the second substrate assembly is located within the housing such that the outer surface of the second substrate assembly is an outer component of the EWOD device; and wherein the EWOD device includes one or more fluid input structures for loading and/or extraction of fluid into/from the channel of the EWOD device; wherein the housing extends around the lateral side edges of the first and second substrate assemblies (82, 84), around only a peripheral portion of the outer surface of the first substrate assembly, and around only a peripheral portion of the inner surface of the second substrate assembly. a first substrate assembly and a second substrate assembly respectively defining an inner surface and an opposing outer surface, wherein the first and second substrate assemblies have opposing inner surfaces; wherein the opposing inner surfaces of the first substrate assembly and the second substrate assembly are spaced apart to define a channel between the opposing inner surfaces of the first and second substrate assemblies, and wherein one of the first or second substrate assemblies (82,84) includes electrowetting electrodes for controlling movement of a droplet of fluid in the channel of the EWOD device; a housing (92, 110) for receiving at least one of the first substrate assembly and the second substrate assembly (82,84), the housing comprising an alignment feature for locating at least one of the first and second substrate assemblies within the housing; and a fixing feature for fixing the at least one of the first and second substrate assemblies within the housing; wherein the second substrate assembly is located within the housing such that the outer surface of the second substrate assembly is an outer component of the EWOD device; and wherein the EWOD device includes one or more fluid input structures for loading and/or extraction of fluid into/from the channel of the EWOD device; wherein the housing extends around the lateral side edges of the first and second substrate assemblies (82, 84), around only a peripheral portion of the outer surface of the first substrate assembly, and around only a peripheral portion of the inner surface of the second substrate assembly.