The first part of this study was the development of a simplified procedure for analyzing laterally loaded piles and drilled shafts. A computer program that can be used to estimate deflections and maximum bending moments in single fixed-head piles (or drilled shafts) and in groups of fixed-head piles (or drilled shafts) was developed. Using this program, charts were developed for estimating deflections and maximum bending moments directly in some of the more common types of single piles and drilled shafts. The computer program was also used to perform parametric studies of groups of piles and drilled shafts, from which simple formulae for amplifying single pile (or drilled shaft) deflections and moments to those of the group were derived. These simple formulae enable the analysis and design of groups of deep foundations to be done more efficiently. The simplified procedure was used to analyze four well documented and well instrumented case histories of laterally loaded pile groups. Comparison of the predicted and measured results indicate that the simplified procedure provides a method of analyzing laterally loaded groups of deep foundations that yield quite accurate predictions of group deflections and moments in some cases, and values that are conservative in other cases. The second part of the research was to establish load factor design procedures for incorporating margins of safety for axially loaded deep foundations. Values of performance factors were developed for load factor design of axially loaded driven piles and drilled shafts. This was achieved by analyzing statistical information for loads and resistances, and determining the levels of reliability inherent in current designs, through the use of probability theory. Using these results, a target reliability level in the form of a reliability index was selected. Values of performance factors were then obtained for use with the current AASHTO (1989) code for bridges and the ASCE Standard 7-88 (1990) for buildings and other structures. The issues involved in a probabilistic analysis of groups of deep foundations were also discussed. / Ph. D.