Numerous ground improvement technologies have been in use for many years on land based projects with various applications. These techniques have provided alternatives that are frequently more affordable and require shorter construction periods than deep foundations. Implementation of these methods in the sea and marine environments is more challenging as specialised equipment is usually either only appropriate for land based projects or have low efficiency and production capability at sea. However, requirement of seabed treatment and improving the characteristics of marine foundations has necessitated the introduction of soil improvement technologies to offshore projects. Some of the ground improvement techniques that have especially evolved to satisfy the requirements of offshore and seabed ground improvement are dynamic compaction, vibro compaction, dynamic replacement, and stone columns. The first two techniques are used for the treatment of granular seabed while the latter two technologies are most appropriate for improving silty and clayey marine foundations. In this paper initially marine and offshore ground improvement techniques with a focus on the mentioned above methods will be discussed. Two case studies of ground improvement for the treatment of soft clays in record water depths will also be introduced. In the first case offshore dynamic replacement was carried out in Southeast Asia at a location where seabed was approximately 30 m below sea level. In the second project stone columns were installed beneath the quay wall and breakwater of the first and second phases of Port of Patras (Greece). The sea depth was up to approximately 40 m and the columns were as long as 20 m.