Clinical guidelines, which can be considered secondary or tertiary sources, combine together the best available and most relevant evidence to provide actionable clinical recommendations. A clinical guideline is a thoroughly-researched and evidence-backed document intended to help healthcare professionals with their decision making, and make evidence-based practice achievable in a busy clinical environment. Clinical guidelines are usually published by authoritative sources, such as professional organizations or major biomedical publishers, and typically follow strict guidelines for how to incorporate and evaluate the evidence they use. Clinical guidelines are often based on secondary sources, such as textbooks, reference texts, and review articles, but may incorporate primary sources as needed.