While high power buck-boost regulators have been extensively researched and developed in the academia and industry, low power counterparts have only recently gained momentum due to the advent of different battery powered and remote electronics. The application life-time of such applications, e.g., remote surveillance electronics can be extended tremendously by enabling energy autonomy. While battery powered electronics last long but they must be replenished once the battery is depleted either by replacing the battery or by retrieving the electronics and then recharging. Instead, energy harvesting from available ambient sources on the spot will enable these electronics continuous operation unboundedly, probably even beyond the lifetime of the electronics. Interestingly enough, recent advancements in micro-scale energy transducers compliment these demand [1-13]. Micro-transducers producing energy from different ambient sources have been reported. These transducers produce enough energy to support a wide range of operations of the remote electronics concurrently. These transducers along with an additional storage elements greatly increase the energy autonomy as well as guaranteed operation since harvested energy can then be stored for future use when harvestable energy is temporarily unavailable. Recently several buck-boost regulators with low power and low input operating voltage have been reported both from academia and industry [14-24]. Some of this work focuses on increasing efficiency in the mid-load range (10mA-100mA), while some other focuses on lowering input range. However, so far no one has reported a buck-boost regulator operating with sub-200nW bias power while harvesting energy from sub-500mV input range. This work focuses on the development of a low voltage low bias current buckboost regulator to attain these goals. In this work, complete design of a PFM mode buck-boost regulator has been discussed in details. Basic topology of the regulator and working principle of the implemented architecture along with the advantages of the specific topology over that of the others have been discussed in short to provide an uninterrupted flow of idea. Later, Transistor level design of the basic building blocks of the buck-boost regulator is discussed in details with different design features and how those are attained through transistor level implementation are discussed. Subsequently, the physical layout design technique and considerations are discussed to inform the reader about the importance of the layout process and to avoid pitfalls of design failure due to layout quality issues. Measurement results are presented with the fabricated IC. Different characterization profile of the IC have been discussed with measured data and capture oscilloscope waveforms. Load regulation, line regulation, efficiency, start-up from low voltage, regulation with line and load transient events are measured, presented and discussed. Different characteristics of the prototype are compared with prior arts and are presented in a comparison table. Die micrograph is also presented along with the different issue of the IC testing