This document discusses statically determinate and indeterminate structures. A statically determinate structure can be analyzed using equilibrium equations alone, while an indeterminate structure has more unknowns than equations. A structure is determinate if the number of reactions r equals 3 times the number of parts n, and indeterminate if r is greater than 3n. Examples are given of determinate and indeterminate structures. Indeterminate structures can be made determinate by removing redundant supports or adding hinges. The advantages of indeterminate structures are that they allow for lighter, more rigid designs with increased safety through redundancy.