THE structural engineer, when designing the construction of buildings to be erected in the area under the jurisdiction of the London County Council, must keep foremost in his mind the requirements of the London Building Acts. These Acts deal primarily with methods of construction and every structural engineer should possess as complete a knowledge of their requirements as he possesses of the principles of structural engineering. To understand the present legislation it is necessary to possess a knowledge of construction in every kind of material. I have always taken it as an axiom "that what is good structural engineering is good building Act,” and this paper will I hope make it apparent that this axiom is true. It has always appeared to me that the principal difficulty in mastering the London Building Act is the lack of information on the earlier Acts which would give the student an opportunity of appreciating the derivation of the principal clauses in their present form. After reading all the Acts relating to building in London which have been placed on the statute book since 1667 I decided to take certain sections in the London Building Act, 1930, and to trace them back to their inception. The results of these investigations were so illuminating to me that I have ventured to offer some of them to you to-night in the form of this paper.