Some researchers have hypothesized that factors common across therapy models are largely responsible for change. In this study we conducted semi-structured, open-ended qualitative interviews with three different MFT model developers (Dr. Susan M. Johnson, Emotionally Focused Therapy; Dr. Frank M. Dattilio, Cognitive-Behavioral Therapy; and Dr. Richard C. Schwartz, Internal Family Systems Therapy), Dr. Johnson and Dr. Schwartz's former students, and each of their former clients who had terminated therapy successfully. We examined possible common factors in our qualitative data analysis. Common factors fell into two main categories of model-dependent factors and model-independent factors. This article--the first of two--reviews the model-dependent common factors, common elements found across three distinct therapies. They include common conceptualizations, common interventions, and common outcomes, each with several subcategories. We discuss the clinical, training, and research implications of the results.