Recent advancements in technologies and increased attention towards renewable energy sources have made offshore wind energy systems as one of the largest and significant electrical power generators. In this chapter, fundamentals of offshore wind energy physics along with resource assessment methodology are described in detail. The process of resource assessment consists of the use of different data sets, different resource and energy estimation models. Wind, being an intermittent resource for power generation, mandates statistical methods to estimate the parameters with uncertainties. Researchers have employed several methodologies to assess offshore wind power density using resource estimation models and geographical information systems. Present chapter will be beneficial in getting familiar with the wind resource data analysis and different aspects of resource assessment.