Experimental investigation of data center cooling and computational energy efficiency improvement through advanced thermal management was performed. A chiller-less data center liquid cooling system was developed that transfers the heat generated from computer systems to the outdoor ambient environment while eliminating the need for energy-intensive vapor-compression refrigeration. This liquid cooling system utilizes a direct-attach cold-plate approach that enables the use of warm water at temperature a few degrees above outdoor ambient to achieve lower chip junction temperatures than refrigerated air. Using this approach, we demonstrated a cooling energy reduction by over 90% and computational energy reduction of up to 14% compared to traditional refrigerated air cooled data centers. To enable future computational efficiency improvements through high-density 3-D-chip stacking, we developed a 3-D compatible chip-embedded two-phase liquid cooling technology where a dielectric coolant is pumped through microscale cavities to provide thermal management of chips within the stack. In two-phase cooling, liquid is converted to vapor, which increases the capacity to remove heat, while the dielectric fluid enables integration with chip electrical interconnects. A test vehicle simulating an eight-core microprocessor was fabricated with embedded cooling channels. Results demonstrate that this volumetrically efficient cooling solution compatible with 3-D chip stacks can manage three times the core power density of today's high-power processor while maintaining the device temperature well within limits.