For self-reconfiguring modular robots the function to autonomously form and break connections between neighboring modules is a defining trait. Connectors must be strong, reversible, transmit power and signal, consume little power, and should be small and light enough for several to fit into each robot module. To make the modular robot system as versatile as possible, the connector should also be genderless, rotation agnostic, and tolerant to misalignment and positioning errors. Traditionally, connectors add significant mechanical complexity to each module. This thesis introduces two hardware components that implement different aspects of the modular robot connection process in small lightweight packages that contain no moving parts: The thermorheological valve is a device for directing fluid flow in order to selectively attract robot modules in a stochastic fluidic self-assembly system. Suitable thermorheological fluids are identified, the mechanical and thermal design of the valve is optimized, and demonstrations of mesoscale thermorheological valves are presented. The soldering connector is a connection mechanism for modular self-reconfiguring robots that forms solder joints by heating a low melting point alloy. The connector is mechanically strong, reversible, electrically conductive, only requires power when connecting and disconnecting, and supports ten to hundreds of connection cycles. Compared to other connection methods for modular robots the soldering connector, which is contained on a single printed circuit board, is very low in complexity, weight, size, and cost. Several designs of the connector are presented and evaluated and general guide- lines for application specific connector designs are provided. The thermorheological valve and soldering connector are then applied in the design of two modular robotic systems. The first proposed application is a fluidic self-assembly system of one-inch-sized, cube shaped modules that rely on stochastic external actuation to form predefined target shapes. Module prototypes and proof-of-concept experiments for this system are presented. A second application implements a system of 40 cube shaped modules that uses the self-soldering connector for self-reconfiguration. Several demonstrations of interactions that mimic the flow of matter through an ecosystem are shown in experiments and simulation, including growth and self-refinement.