Measurement of Invariant Differential Cross Sections and Ratios of Identified Charged Hadron in p-p Collisions at RHIC The invariant cross sections and ratios of identified mid-rapidity charged hadrons have been measured as a function of transverse momentum in p-p collisions at $\sqrt{s_{NN}} = 200$ GeV by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC). The charged hadron sample; namely, $\pi^{\pm}$, $K^{\pm}$, p, and $\bar{p}$ were identified by a high resolution Time-of-Flight scintillator wall. The differential invariant cross section is fundamentally important for understanding particle production mechanisms in p-p collisions. Furthermore, the invariant cross section of identified charged hadrons provides a baseline measurement for carefully examining the underlying nuclear effects in d-Au and Au-Au reactions. Hence, a detailed study of the nuclear modification factor, $R_{AA}$, and Cronin effect may be determined by direct comparison to p-p reactions. The p-p cross sections and ratios will be shown and compared to both the d-Au and Au-Au results as a function of the transverse momemtum.