The U.S. healthcare system is a complex segment of our society that is constantly evolving with changes to various areas such as education, financing, safety, and health. There continues to be a critical examination of how healthcare professionals are trained and utilized as healthcare demands increase. One category of healthcare professionals that has evolved over time to address societal needs is pharmacists. Pharmacists have kept their traditional function of dispensing medications while expanding into multiple areas of expertise and training from patient counseling and drug therapy, to being part of multidisciplinary teams treating acute care patients. According to the National Association of Boards of Pharmacy (NABP) in 2009 there were approximately 265,000 licensed pharmacists in the U.S. (NABP, 2010). The Health Resources and Services Administration (HRSA) reported the settings with the largest number of positions are chain pharmacies (77,300), hospitals (49,200), and independent pharmacies (36,200) (DHHS, 2008). The ratio of pharmacists per 100,000 population is expected to increase from 68.9 pharmacists per 100,000 population to 76.7 per 100,000 between 1995 and 2020 (Gershon, Cultice, & Knapp, 2000). This increase in the pharmacist to population ratio is consistent with a growth rate of 13% during this time period of time. Until 1998, the supply of pharmacists in the U.S. appeared to be in reasonable balance with demand. Market forces gradually upset the delicate balance between the supply of pharmacists and the demand for their services between 1998 and 2009. In particular, a precipitous increase in the volume of prescription written and filled during this time period contributed to upsetting this delicate balance between the supply of pharmacists and demand (Cooksey, Walton, Stankewicz, & Knapp, 2003). Researchers have noted a number of environmental factors affecting the pharmacist supply in the U. S. This inquiry explores these factors within the context of the population ecology theoretical framework. In addition to the volume of prescriptions, additional environmental factors believed to have a discernible impact on the pharmacist supply include, the number of physicians, size of the business industry and insurance coverage. Previous studies on pharmacists supply have pointed to income, physician population, and population among other variables that predict the demand for pharmacists (Walton, Cooksey, Knapp, Quist, & Miller, 2004; Cherry, D.K., Woodwell, D.A., & Rechtsteiner 2007; Walton, Knapp, Miller, & Schumock 2007). U. S. physicians wrote over 4 billion prescriptions in 2007 (Medical Expenditure Panel Survey, 2008). Physicians are the primary healthcare providers that generate prescriptions to be filled. Consequently, the number of physicians is believed to be a significant environmental factor affecting the supply of pharmacists. There were approximately 940,000 physicians in the U. S. in 2008. Projections call for continuous growth of the number of physicians well into the future (Smart, 2010). Another important environmental factor potentially impacting the demand for pharmacists is the size of the business industry. In 2006, the health plan offer rate for large or medium organizations (50 or more employees) was 96.7% compared to 61.2% for small organizations (50 or less employees) (Sommers & Crimmel, 2008; Crimmel & Sommers, 2008). Insurance cov¬erage has the potential to have a positive impact on the demand for pharmacists because it provides the opportunity to obtain required prescriptions (Ranji, Wyn, Salganicoff, & Yu, 2007; Weinick, Byron, & Bierman, 2005). The population ecology theoretical framework has been used in the study of restaurants, newspapers, and physicians and their interactions with their surrounding environments. The theoretical framework proved to be beneficial in the exploration of the pharmacist supply vis-á-vis the environment. The primary constructs in the population ecology theory are carrying capacity and density. Carrying capacity consists of two sub-constructs: munificence and concentration. Density points to the current pharmacists supply and its impact on the future pharmacist supply. Numerous variables have been used in previous empirical studies of the pharmacist supply. Among the indicators of munificence in previous studies in the extant literature on pharmacist supply are total population, elderly population, hospitals, and median household income. In the present inquiry, total population was found to be a statistically significant environmental factor affecting the pharmacist supply. This was hypothesized that there is a positive linear relationship between total population and the pharmacist supply. The number of hospitals with pharmacies was also found to be a statistically significant environmental factor affecting the pharmacist supply. Hospital pharmacies are important venues wherein pharmacists can demonstrate their unique expertise and make discernible contributions to desirable health care outcomes when pharmaceutical interventions are required. In light of this empirical finding, it seems reasonable that a growth in hospital pharmacies corresponds with an increased demand for pharmacists (Kaboli, Hoth, McClimon, & Schnipper, 2006). Measures of the concentration dimension included the number of hospital beds per 100,000 population, employer volume and size and the number of insured. The only putative indicator of concentration that was found to be statistically significant in this inquiry was the number of employers with 20 or more employees. Previous pharmacist supply was found to be a significant environmental factor affecting the pharmacist supply in the future. Thus, density is a significant environmental factor affecting the pharmacist supply. Five of the 13 hypotheses tested in this inquiry were accepted. These findings are consistent with related findings in the extant literature on the pharmacist supply. Empirical findings from this inquiry are believed to make significant contributions to the literature on the pharmacist supply. The population ecology theoretical framework appears to be a suitable tool for exploring environmental factors affecting the pharmacist supply. Recommendations for future research are presented in the final chapter.