The objective of this review was to examine the characteristics and processes of clinical reasoning used by registered nurses in clinical practice, and to identify factors reported to relate to the use of clinical reasoning by registered nurses in clinical practice. Significant variability in the clinical reasoning of graduate registered nurses has been identified in research, with underdeveloped and unsafe clinical reasoning being linked to failure-to-rescue and sentinel events in the clinical setting. The identification of characteristics and processes of clinical reasoning, and factors relating to registered nurses' clinical reasoning when engaged in clinical practice, will increase understanding of the clinical reasoning requirements for undergraduate registered nurses and of potential factors that may affect their clinical reasoning. Studies including registered nurses who met the criteria for registered nurse registration in Australia and who used clinical reasoning to engage with health care consumers in all practice environments were eligible for inclusion. Eight databases were searched, with articles identified through CINAHL, MedNar, PubMed, Science Direct, ERIC, PsycINFO, Scopus, and ProQuest Dissertations and Theses. Database searches were conducted on December 31, 2020, and updated August 20, 2021, with primary qualitative and quantitative research studies in English from 2000 onwards considered for inclusion. Opinion papers, text, and reports were not included. Data were extracted based on the draft charting tool from the scoping review protocol, with results presented in tabular format and in a narrative summary. The 29 qualitative and 5 quantitative research studies included in the scoping review utilized exploratory descriptive, descriptive rationalist, narrative, ethnography, correlational, observational, and grounded theory methodologies in their research designs. Observation, think-aloud sessions, questionnaires, surveys, interviews, and focus groups were used to collect data from the 1099 participants in 9 countries. Multiple concepts related to the characteristics (n=35) and processes (n=30) of clinical reasoning were detected in the research studies, with 5 categories identified: i) situation management, ii) data management, iii) interpreting, iv) implementing and evaluating, and v) professional practice, with an additional processes category identified (decision-making processes). The factors (n=26) reported to relate to clinical reasoning were categorized into environment of care, care requirements, professional practice, experience, knowledge, and decision-making processes. Connections between the various concepts were evident throughout the review. The scoping review identified characteristics and processes of clinical reasoning, as well as factors reported to relate to clinical reasoning in all studies. The concepts that comprise the clinical reasoning of registered nurses in clinical practice must be considered in undergraduate registered nurse education. Registered nurses must complete their baccalaureate program with well-developed clinical reasoning to ensure safe clinical practice. Understanding the characteristics and processes of registered nurses' clinical reasoning in clinical practice, and the factors reported to relate to clinical reasoning, supports the creation of targeted resources for development and assessment of clinical reasoning.