SIENA is a program for the statistical analysis of network data, with the focus on social networks.
Networks here are understood as entire (complete) networks, not as personal (egocentered) networks: it is assumed that a set of nodes (social actors) is given, and all ties (links) between these nodes are known - except perhaps for a moderate amount of missing data.
SIENA is designed for analyzing various types of data as dependent variables:

Longitudinal network data:

This refers to repeated measures of networks on a given node set (although it is allowed that there are some changes in the node set). Models can be specified with actor-oriented as well as tie-oriented dynamics.

Longitudinal data of networks and behavior:

This is like longitudinal network data, but in addition there are one or more changing n odal variables that are also treated as dependent variables, and referred to as behavior. The network will influence the dynamics of the behavior, and the behavior will influence the dynamics of the network. In other words, this is about the co-evolution of networks and behavior.

Cross-sectional network data.

'Cross-sectional' means that only one observation is available. This method uses exponential random graph models ('ERGMs'), also called p* models.
The ERG model is implemented in SIENA version 3, but not any more in version 4 (RSiena).

The main approach used by SIENA for modeling dynamics of network (or of networks and behavior) is an actor-oriented model, in which it is assumed that the social actors who are represented by the nodes in the network play a crucial role in changing their ties to other actors; in the case of associated behavior dynamics, also in changing their behavior. As an alternative, tie-oriented models are also available. All of these models are Markov chain models; such models are more applicable to relations and behavioral variables that can be regarded as states than to relations or behavior that are more adequately regarded as non-enduring events.

Both for longitudinal and for cross-sectional modeling of networks, the statistical analysis in SIENA is done on the basis of computer simulation of the network. This can be time consuming. In view of the detailed approach to network dynamics and the required computing resources, the method is applicable in principle to networks on approximately 10 to 1,000 nodes.

The methods implemented in SIENA are described in the papers given in the webpage with literature. Some further articles with applications are given in the webpage with further applications. The program and the extensive manual can be obtained from the downloads webpage.

There exists a User Group for Siena and StOCNET to exchange information and seek technical advice on using the Siena and StOCNET software to analyze network data.
The address is http://groups.yahoo.com/groups/stocnet/.

SIENA version 3 is written in Delphi, for use under Windows.

SIENA version 4 is also called RSiena, a contributed package for the R statistical system, which can be downloaded from http://cran.r-project.org.
RSiena can be used in two ways: for those who do not have knowledge of how to operate R (or do not wish to use this knowledge), it is possible to operate RSiena through a graphical user interface which works apparently independently of R. For R users, it is also possible to operate RSiena through commands as is usual for other R packages.
The incorporation of RSiena in R makes available all other possibilities offered by R; in particular, to execute R in a Mac or Unix/Linux environment. Further information on RSiena is on the RSiena page.

The release of RSiena marks a step in the transition from the Windows-based SIENA 3 to the R-based, multi-platform SIENA 4. The transition is not yet complete, in the sense that not yet all intended functionalities of SIENA 3 have been implemented for SIENA 4. The latter program only will contain procedures for the analysis of longitudinal network data, not those for analyzing Exponential Random Graph Models (ERGMs). Further work on the StOCNET interface will be discontinued, as this is functionally replaced by the graphical user interface of RSiena.

The newest official release (June, 2007) of SIENA 3 is version 3.11. This release is included in the newest (July, 2007) version of StOCNET. Beta releases are quite frequent. Newest releases of version 3 can be downloaded from the downloads page.

For the meta-analysis (or multi-group analysis) of several data sets analyzed by SIENA, methods can be found at the webpage of the program SIENA08.

Known bugs and new papers are given at the news webpage.

The SIENA program is part of an ongoing research effort. The research team is composed of Tom Snijders, Christian Steglich, Ruth Ripley, Johan Koskinen, and Krists Boitmanis, with contributions from Michael Schweinberger, Mark Huisman and Marijtje van Duijn. Current research projects are given at the research projects webpage. Courses and a user group are mentioned at the activities webpage.

The SIENA 3 program can be executed in two ways. Many people find it convenient to execute it from the StOCNET environment. It is also possible to execute SIENA as a stand alone program. The StOCNET project is an activity of Christian Steglich, Tom Snijders, and SciencePlus (Minne Oostra), with important earlier contributions from Evelien Zeggelink, Peter Boer, Bert Straatman, Mark Huisman, and others.