Explaining tropospheric ice number concentrations and well establishing the contributing formation mechanisms remains a grand challenge in cloud microphysics, leaving a knowledge gap for model development. Advances over the past decade have reduced uncertainties in measuring ice and ice-nucleating particle (INP) spectra, expanded remote-sensing retrieval capabilities, and furthered evidence for the likely commonality of secondary ice production (SIP). We invite presentations that aim to document the occurrence of secondary versus primary ice formation in observations (including in situ and ground- and satellite-based remote sensing), quantify the relative contributions of various secondary and primary mechanisms (including homogeneous drop and aerosol freezing, INP activation, and ice multiplication) to the ice found in cold clouds of all types (including convective, mixed-phase stratiform, and cirrus) using observations and/or models (including climate, cloud-resolving, and idealized), and better establish secondary or novel ice formation mechanisms via laboratory studies (including via hydrometeor collision, drop freezing, etc.).