Within the evidence-based movement means are developed to support the practitioner in becoming a research consumer with knowledge and skills to create an evidence-based practice (EBP). But little is actually known about whether, and how, this evidence-based accumulation of knowledge is used by practitioners and in what way any actual use leads to improved outcomes. Clinical practice guidelines (CPGs) are described to provide means to keep up with scientific development and may serve as an interface between science and practice. Implementation of evidence and guidelines in daily care are very complex and knowledge about the best way to implement evidence to facilitate best practices is still limited. The overall aim of this thesis was to explore factors that influence an evidence-based clinical practice, and more specifically, to investigate outcomes of an evidence-based practice, the dissemination and awareness of evidence-based literature, and to describe factors of importance when implementing CPGs. A systematic review was conducted to identify outcomes, and different experimental designs have been used for the purpose of describing awareness and dissemination of evidence-based literature as well as experience of the implementation of CPGs. Furthermore, a test-retest was conducted to test the reliability of items constructed from factors drawn from The Promoting Action on Research Implementation in Health Services (PARIHS) framework.The findings of the systematic review showed that it is difficult to prove effects of an EBP and the studies that managed this had implemented evidence-based CPGs. Although improvements in outcomes were reported for patients, personnel and the organisation, the synthesis showed a weak scientific foundation for the overall result since the studies included were heterogeneous in their designs. In a questionnaire study, in the area of psychiatric nursing with a pre-post design in relation to published evidence-based nursing reports, some differences were detected over time. But still 39.5 % of the sample reported no access to evidence-based literature one year after the publication of the two evidence-based nursing reports, and few of the respondents who had access to evidence-based literature reported any use of it. In the test-retest items of factors such as clinical experience, patients experience, leadership, context, culture, evaluation and facilitation was included. The findings of the test-retest showed that the reliability varied from good to fair agreement regarding the Kappa values, with a predominance of moderate agreement. The interview study, with an interpretive qualitative design, revealed several factors that appeared to be of importance for the implementation CPGs. The factors seemed to form a base consisting of circumstances, conditions and requirements. These have a relation to components that constitute a process, thus illustrating that implementing CPGs are continuous processes of creating reliable and tenable routines which involve all staffs member and are expected to lead to better and safer care of patients and increase knowledge and confidence among the staff.In conclusion, it is complicated, but not impossible, to demonstrate the outcomes of an EBP. To implement evidence-based CPGs is one way to make an evidence-based care visible. But more research is needed to strengthen the scientific foundation and to establish whether the tendency towards improved outcomes reported can be further supported. To implement CPGs is described as processes of bringing about a certain level of best practice that benefits patients as well as the staff. There are several factors influencing the process in relation to both positive and negative aspects and depending on which aspects will rise in the foreground the processes are visible or concealed, move forward or stagnate, promote or impede a successful implementation.