Geothermal energy has been used for recreational purposes for millennia, but its exploitation for generating electricity started just over a century ago. Although geothermal energy is unique among renewable energy sources due to its basic capabilities and the ability to supply heat from renewable sources, its exploitation still significantly falls behind other renewable sources. This can be mainly attributed to uncertainty regarding the availability of resources in poorly explored deposits and financial expenditures at an early stage of exploration. Advances in reservoir characterization techniques are beginning to narrow the limits of exploration uncertainty, both by improving the estimates of reservoir geometry and properties and by providing temperature estimates at depth before drilling. Advances in drilling and management technologies can potentially significantly reduce start-up capital, while operating costs are further reduced by more efficient reservoir management and increasingly efficient energy conversion systems. Increased awareness of the benefits of geothermal energy along with technological advances can lead to geothermal energy becoming a major type of a renewable energy technology.