This paper demonstrates that aesthetic concepts in engineering design are derived from various models of aesthetics. It also presents case studies on the application of the golden ratio in various structures. The aesthetic perceptions of various respondents who are shown families of rectangles, three span bridges and parallel chorded trusses are described. The preferences for a square or ratio of unity and for the golden ratio are discovered from these experiments. The study also includes approximate optimisation studies on the three span bridge and parallel chorded trusses. Finally, the possibility is mooted of making initial design decisions relating to proportions, by using plots of cost optimisation and aesthetic preferences. C. Kulasuriya, BSc(Eng), MEng Professor W. P. S. Dias, PhD, DIC, MlStructE M. T. P. Hettiarachchi, MSc, PhD, DIC Department of Civil Engineering, University of Moratuwa, Moratuwa, Sri Lanka