Designing fixed offshore structures and floating units involves complex engineering and poses significant scientific challenges. Correctly predicting the environmental forces at play –wind and current loads - is critical in the design and engineering stage and effects a range of factors including stability, fatigue, mooring, dynamic positioning, and towing resistance. Accurately calculating loads is vital to ensuring safe operation throughout the design life of an offshore facility. The methods used - ‘building block’ approaches, Computational Fluid Dynamics (CFD), and Wind Tunnel testing - will be highlighted, with advice provided as to when each should be considered. Case studies will showcase the value of detailed studies and consultation throughout the design lifecycle.