Clinical judgment, defined as "the application of the nurse's knowledge and experience in making decisions about client care" (The National Council of State Boards of Nursing, 2005, p. 2), has been recognized as a vital and essential skill for healthcare providers when caring for clients. Undisputedly, nurses represent the largest component of the healthcare profession and, therefore, play a major role in ensuring quality patient care in the United States. Although the concept of clinical judgment in nursing has been discussed for more than three decades, and in spite of numerous efforts to improve student clinical judgment, the recent literature indicates that most new graduate nurses do not meet expectations for entry-level clinical judgment ability. The overall goal of this project was to investigate the feasibility of using Brunswik's Lens Model in the development of a quantitative instrument to measure clinical judgment in senior level nursing students. A newly designed instrument, Clinical Judgment Assessment (CJA) Instrument, was developed specifically for this study. A paper and pencil assessment was conducted, using two case vignettes based on authentic patients to measure clinical judgment of senior nursing students. Nurse expert responses served as criteria for the measure. A convenience sample of 250 senior nursing students in baccalaureate and associate degree nursing programs were recruited from approved nursing programs in the Southern Nevada area. Content validity of the instrument was reflected through the use of concept analysis, expert opinion, and the content validity index (CVI). The CVI for the instrument as rated by the experts reflected 0.86 to 1.00 for items designated as "important." Reliability of the instrument was estimated using Cronbach's alpha and test-retest procedure. The scores from the test and the retest were calculated using Cohen's Kappa and found the statistical significance of Kappa (p less than 0.05) at 0.750 for the medical case and 0.799 for the surgical case. For the adjusted CJA instrument, reliability coefficients (alpha) of 0.879 and 0.892 were found for the medical and the surgical case, respectively. The final number of items in the CJA instrument was 172. The composite (CJA) scores, calculated by the formula proposed in this study, of students and experts were analyzed ("t"-test) and found a statistically significant difference (p less than 0.05) between the two groups. This finding provided support to the validity of the CJA Instrument. This study provided an initial understanding of the measurement of clinical judgment. Recommendations for further study include further establishment of the criteria for the instrument through administration to a larger sample of nurse experts. A web-based format is recommended due to the complexity of the assessment and the scoring. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]