Contribution of Douglas North to the general institutional economic theory is considered with a special emphasis on the research of institutional factors of economic changes. It is shown how agents interaction models are formed and how institutions influence the agents’ behaviour and change of their models and behaviour reactions. It is especially important, that D. North’s conclusions and their development in modern economic theory result in emergence of the so-called institutional macroeconomics. As a scientific discipline it explains economic changes on long intervals of evolution. This possibility is formulated in D. North’s works on the history of economic changes, where institutions are of importance. The basic emphasis in the article is made on two D. North’s works: “Institutions, Institutional Changes and Economic Performance” (1990) and “Understanding the Process of Economic Change” (2005) which have much in common, though they were written at different time. At first, the general outline of D. North’s theory of economic/institutional changes is given, then the author’s treatment concerning institutions and agents interaction is presented. The analysis of intellectual force of the formula of inclusion of institution of trust in macroeconomic analysis is given. Pluses and probable minuses of new institutional approach of D. North on a long interval of social evolution are shown.