star formation that have been made using SPH. In Section \[jeansmass\], we discuss the importance of always resolving the Jeans mass in numerical studies of self-gravitating gas. While this has been demonstrated using various types of hydrodynamic code, we concentrate specifically on the problems that can arise if this criterion is not obeyed with SPH. In Section \[collstellar\], we demonstrate that, for the first time, it is now possible to perform three-dimensional hydrodynamic calculations which follow the collapse of a molecular cloud core to stellar densities. These calculations are performed with SPH. Finally, in Section \[accretion\], we discuss how SPH has been used to study the evolution of a protobinary system as it accretes from an infalling gaseous envelope and how this work can lead to predictions of the properties of binary stars.

The Importance of Resolving the Jeans Mass {#jeansmass}
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It has recently been realised that it is important that the Jeans mass/length is always resolved during a hydrodynamical calculation. This has been demonstrated both with SPH [@BatBur97; @Whitworth98] and with grid-based codes [@Trueloveetal97; @Trueloveetal98; @Boss98]. If this criterion is not obeyed, artificial fragmentation can be induced, or fragmentation can be inhibited. Essentially this is because when the 