Active resistors in VLSI technology have grown in stature as they enable the design of large resistive loads without using excessively bulky resistors, or a high voltage supply. Active resistors designed in CMOS technology have the property of being voltage controlled, which permits the design of negative resistance circuits. A negative resistance circuit has the property in which the current is a decreasing function of the input voltage, and has an I-V curve with a negative slope. They have the potential of being a key building block for larger electronic systems in VLSI technology, with applications in various fundamental circuits such as amplifiers and oscillators.  A detailed characterization of negative resistance circuits is presented in this thesis. Important large and small signal characteristics, including noise, linearity and power consumption are investigated. A strategy for designing wide bandwidth active resistors is proposed with supporting analysis. Key stability issues that have not previously been reported are brought forward and the stability of larger circuits that accommodate a negative resistor are investigated. To conclude the thesis, design applications in which negative resistors have been used to improve the performance of larger electronic systems are demonstrated. These include the design of a low phase noise current mode oscillator and a high bandwidth inverting feedback amplifie