This thesis describes an analysis of modern jack-up designs. Trends throughout the various designs are identified and justified. The environmental loads and dynamic response of these modern designs are analysed using the methodology as described in current guidelines. Furthermore, the water depth limit of current design philosophy is investigated. This research shows that as water depths increase, jack-ups become more wind-dominated in terms of environmental loading. A more detailed wind load calculation method, than the currently used projected-area method, is therefore recommended. Furthermore the need for increasing chord spacing is identifed in an attempt to retain a stiffness dominated structure. This however increases the risk of problems associated with Rack Phase Difference (RPD) which occur during jacking operations and therefore illustrates a conflict within the design of jack-ups as the industry heads for deeper and deeper waters.