The Gordon Research Conference on Molecular and Ionic Clusters focuses on the study of molecular aggregates and the fundamental molecular physics underpinning their structure, dynamics, and optical properties. Cluster science involves a highly collaborative community of experimentalists and theorists from a broad array of disciplines, such as biophysics, aerosol science, materials science, astrochemistry, and molecular physics. Clusters provide a means by which intermolecular forces and cooperative effects can be probed as a chemical system evolves from single atoms and molecules to bulk matter. Cluster studies have lead to fundamental insights into aggregation processes that lead to aerosol formation in the troposphere, conformational preferences and dynamics in biological macromolecules, heterogeneous chemical phenomena in the interstellar medium, and the origin of catalytic behavior in inorganic nanoparticles. Sessions in this GRC explore recent theoretical and experimental innovations that allow for a detailed molecular-level study of the size-dependent chemical and physical properties associated with cluster systems. Systematic studies of cluster systems are carried out with state-of-the-art laser-based spectroscopy methods (spanning the far IR to VUV and X-ray regions of the electromagnetic spectrum), high resolution mass spectrometry techniques, photoelectron and velocity map imaging spectroscopies, terahertz and microwave spectroscopies, X-ray diffraction imaging, helium nanodroplet isolation, liquid jets, and sophisticated ion-trapping techniques. In addition, time-resolved techniques are applied to cluster systems to probe dynamical phenomena related to electron and nuclear motion and relaxation. This diverse array of experimental methods produces molecular-level information that can be compared directly to the predications of state-of-the-art theoretical methods. The synergistic combination of experiment and theory is especially relevant to the field of cluster science. This GRC highlights emerging computational approaches for exploring complex intermolecular potential energy surfaces and the photochemistry of cluster systems. The presentations at this GRC will feature invited talks, contributed oral presentations on late-breaking topics and poster sessions.