Assemble proposes an intuitive graphical interface to study and construct complex three-dimensional RNA structures. When an RNA tertiary structure is opened with Assemble, it is automatically annotated with a secondary structure definition. This secondary structure can be used as a map to analyze the original tertiary structure. Using a secondary structure definition, Assemble can also produce a first draft of a 3D Model. Then the construction process can be pursued "by hand" using several widgets.