Clinical evidence technologies (CETs) are information sources derived from medical research literature that may assist health care providers in continued learning, decision-making, and patient care. Examples of CETs include: MEDLINE/PubMed and Cochrane Reviews, research journal literature, print and electronic medical texts, clinical topic summaries, guidelines, and interactive decision tools. Clinicians utilize CETs to find answers to questions that arise during patient care. However, it was unclear if CETs had a measurable impact on provider practice or patient outcomes. A literature review identified twenty-two articles evaluating CETs' impact. Study designs included surveys, observational studies, randomized controlled trials and quasi-experimental methods. The review revealed mixed evidence of CET impact on provider-level outcomes such as improved diagnoses and treatments, and on patient level outcomes such as length of hospital stay and mortality. Additional research was needed to determine whether certain CETs or CET types have impact on patient care outcomes in clinically targeted areas. We conducted a cluster-randomized controlled trial (CRCT) to evaluate the effect of a dermatology-focused CET (VisualDx) when used by primary care providers. We found no difference in the patient skin disease outcomes of resolution of symptoms and return visits for the same problem in that trial. Thirty-two PCPs and 433 patients participated. In proportional hazards modelling adjusted for provider clusters, the time from index visit to skin problem resolution was similar in both groups (Hazard Ratio=0.92; 95% Confidence Interval (CI)=0.70, 1.21; P=0.54). Patient follow-up appointments did not differ significantly between groups (Odds Ratio=1.26; CI=0.94, 1.70; P=0.29). In a follow up mixed-methods study, we sought to understand why VisualDx did not make a difference. All CRCT provider participants were surveyed about their experience in the trial. VisualDx users (intervention arm) were interviewed about their experience using the CET. Ease of access and usefulness for patient communication facilitated successful use while irrelevant search results and use of other sources were barriers. Although PCPs reported benefits, they did not perceive the CET as useful often enough to motivate using it frequently or exclusively, thereby reducing the likelihood of it making a difference in the problem resolution and return appointment outcomes. There was no difference in skin problem resolution or number of follow-up visits when PCPs used VisualDx. PCPs did not perceive VisualDx as "useful" often enough for to use it frequently, or exclusively, thereby reducing the likelihood of this CET making a difference in patient-level outcomes.