We present a Java toolkit for the procedural construction, validation, and marshalling and unmarshalling for METS. METS, the Metadata Encoding & Transmission Standard, is intended to provide a standardized XML encoding for transmission of complex digital library objects between systems. While it provides standard containers and encoding mechanisms for descriptive and administrative metadata, it does not define the content or format of that metadata. However, the content and format of structural metadata is explicitly mandated within the METS specification.