The problem of fault detection and location in modular tree structures are considered in this thesis. The fault set is restricted to stuck-at-faults in the discussion of the fault location problem. Short circuit faults and broken and short circuit faults are considered in the discussion of the fault detection problem. In either the fault detection or location case, detection conditions for each fault in a cell are derived. Tests for locating or detecting fault are designed based on providing those detection conditions to each cell in a tree. For fault detection, the more detection conditions provided by a test, the better the test is. The detection conditions provided by the detection test must be partitioned into single element blocks to locate faults. In this thesis, two algorithms in for fault detection and three for fault location in a combinational modular tree with n input variables are presented in detail. All the above results are directly modified for fault detection and location in modular trees which realize arbitrary definite machines. Since a pair of these tree structures can be connected to realize arbitrary sequential machines, the results derived here are useful in diagnosing sequential machines. / Master of Science