This article introduces the idea of employing dynamic spectrum management to passive optical network systems. The primary motivations of this system are to enhance the bandwidth, split ratio, and loss budget of existing PONs, without mandating the replacement of the ONU and passive optics. The technical issues to be overcome in DSM-PON are considered, including management of the ONUs' spectral distribution and various filter designs. Several system applications of the scheme are suggested that have good practical and economic benefits.