Organic chemists entering the field of synthetic ion channels and pores are often restricted to the characterization of their creation by fluorescence kinetics in vesicles and do not have access to conductance experiments in planar bilayer membranes. This limitation excludes the application of methods to evaluate key characteristics such as ion selectivity or voltage gating that are routine in the membrane biophysics community. The objective of this account is to offer to the non-expert an introduction to the assessment of ion selectivity in vesicles with examples from years of research on functional rigid-rod molecules in biomembranes.