This talk suggests that star forming environments should be classified into finer divisions than the traditional isolated and clustered modes. Using the observed open cluster system and theoretical considerations of cluster formation, we estimate that only 10% of the stellar population originates from star forming regions destined to become open clusters. The smallest clusters included in the observational surveys (with at least N = 100 members) roughly coincide with the smallest stellar systems that are expected to evolve as clusters in a dynamical sense. We show that stellar systems with too few members (N < N*) have dynamical relaxation times that are shorter than their formation times (1-2 Myr), where the critical number of stars N* = 100. Our results suggest that star formation can be characterized by (at least) three principal modes: [I] isolated singles and binaries, [II] groups (N less than N*), and [III] clusters (N greater than N*).

Next, we turn attention to our own solar system. Using its observed properties, we constrain the star formation environment of the Sun within the scenario of (external) radioactive enrichment by a massive star. This calculation yields a probability distribution for the number of stars in the solar birth aggregate. The Sun is most likely to have formed within a stellar group containing ~2000 members. Only about 1 out of 120 solar > systems are expected to form under similar conditions. We discuss additional implications of this scenario, including possible effects from the radiation fields provided by the putative cluster environment and dynamical disruption of the Kuiper Belt.