A mixed-signal reconfigurable platform gives the designer the choice of implementing systems using the benefits of both analog and digital circuits. The subject of this research is the implementation and application of mixed-signal reconfigurable systems utilizing floating-gate transistors and field programmable analog/digital arrays. Basic analog circuits using floating-gate CMOS devices have been developed for this research. Floating-gate based analog circuits reduce the effects of inherent property mismatch present in analog circuits. Various circuit blocks including current mirrors, gilbert multipliers, and $G_m-C$ filters were designed and experimentally demonstrated to show reduced mismatch effects. Such floating-gate transistors and circuits are the basis for the reconfigurable systems developed in this research. To enable high-performance reconfigurable systems, sub-micron and sub-$100 nm$ CMOS process nodes were used in this research. Scaling of Floating-gate devices is a key issue at small nodes. Test structures were created to verify the programming capability for floating-gate devices at various process nodes. Experimental results show scalability of floating-gate devices along with effective charge programming ability. A floating-gate based reconfigurable mixed-signal platform using Field-Programmable Array of Analog-Digital Devices (FPAADD) has been created and experimentally verified. Further FPAADD systems augmented with a CPU based digital back-end were developed to enable greater applications for such reconfigurable systems. Experimental functionality and circuits/systems created using FPAADD based systems were demonstrated for this research work.