This chapter from Volume 1 of "Research-Based Reform of University Physics" describes an interactive method of teaching, Investigative Science Learning Environment (ISLE), that helps students learn physics by engaging in processes that mirror the activities of physicists when they construct and apply knowledge. These processes involve observing, finding patterns, building and testing explanations of the patterns, and using multiple representations to reason about physical phenomena. ISLE is a comprehensive learning system that provides a general philosophy and specific activities that can be used in "lectures" (interactive meetings where students construct and test ideas), recitations (where students learn to represent them in multiple ways while solving problems), and labs (where students learn to design their own experiments to test hypotheses and solve practical problems). In ISLE, students are assessed for conceptual understanding, for problem-solving ability, and, most importantly, for their use of various scientific abilities. ISLE includes activities that help students acquire some of the abilities used by scientists in their work: experiment design, model building, use of multiple-representations, evaluation, etc.  A set of rubrics is available that can be used by instructors for grading and by the students for self assessment. This chapter also provides a theoretical basis for the ISLE structure (using brain and cognitive research), explains how this learning system addresses the needs of the 21st century science education and workplace, and outlines how it is different from other reformed curricula.