Apache Tomcat 6.x. Apache Tomcat 6.x is the current focus of development. It builds upon the improvements made in Tomcat 5.5.x and implements the Servlet 2.5 and JSP 2.1 specifications. In addition to that, it includes the following improvements:

* Memory usage optimizations
* Advanced IO capabilities
* Refactored clustering

Apache Tomcat 5.5.x. It supports the same Servlet and JSP Specification versions as Apache Tomcat 5.0.x, there are significant changes in many areas under the hood, resulting in improved performance, stability, and total cost of ownership. Please refer to the Apache Tomcat 5.5 Changelog for details.

Apache Tomcat 5.0.x. Apache Tomcat 5.0 improves on Apache Tomcat 4.1 in many ways, including:

* Performance optimizations and reduced garbage collection
* Refactored application deployer, with an optional standalone deployer allowing validation and compilation of a web application before putting it in production
* Complete server monitoring using JMX and the manager web application
* Scalability and reliability enhancements
* Improved Taglibs handling, including advanced pooling and tag plugins
* Improved platform integration, with native Windows and Unix wrappers
* Embedding using JMX
* Enhanced Security Manager support
* Integrated session clustering
* Expanded documentation

Apache Tomcat 4.x implements a new servlet container (called Catalina) that is based on completely new architecture. The 4.x releases implement the Servlet 2.3 and JSP 1.2 specifications.

We encourage all users to upgrade to Apache Tomcat 5.x whenever possible.

Apache Tomcat 4.1.x. Apache Tomcat 4.1 is a refactoring of Apache Tomcat 4.0.x, and contains significant enhancements, including:

* JMX based administration features
* JSP and Struts based administration web application
* New Coyote connector (HTTP/1.1, AJP 1.3 and JNI support)
* Rewritten Jasper JSP page compiler
* Performance and memory efficiency improvements
* Enhanced manager application support for integration with development tools
* Custom Ant tasks to interact with the manager application directly from build.xml scripts

Apache Tomcat 4.0.x. Apache Tomcat 4.0.6 is the old production quality release. The 4.0 servlet container (Catalina) has been developed from the ground up for flexibility and performance. Version 4.0 implements the final released versions of the Servlet 2.3 and JSP 1.2 specifications. As required by the specifications, Apache Tomcat 4.0 also supports web applications built for the Servlet 2.2 and JSP 1.1 specifications with no changes.

We encourage all users to upgrade to Apache Tomcat 5.x whenever possible.

here are several versions of Apache Tomcat 3.x currently available for download:

* Version 3.3 is the current production quality release for the Servlet 2.2 and JSP 1.1 specifications. Apache Tomcat 3.3 is the latest continuation of the Apache Tomcat 3.x architecture and it is more advanced then 3.2.4, which is the ‘old’ production quality release.
* Version 3.2.4 is the ‘old’ production quality release and is now in maintenance only mode.
* Version 3.1.1 is a legacy release.

All Apache Tomcat 3.x releases trace their heritage back to the original Servlet and JSP implementations that Sun donated to the Apache Software Foundation. The 3.x versions all implement the Servlet 2.2 and JSP 1.1 specifications.

Apache Tomcat 3.3.x. Version 3.3.2 is the current production quality release. It continues the refactoring that was begun in version 3.2 and carries it to its logical conclusion. Version 3.3 provides a much more modular design and allows the servlet container to be customized by adding and removing modules that control the processing of servlet requests. This version also contains many performance improvements.

Apache Tomcat 3.2.x. Version 3.2 added few new features since 3.1; the major effort was a refactoring of the internals to improve performance and stability. The 3.2.1 release, like 3.1.1, was a security patch. Version 3.2.2 fixed a large number of bugs and all known specification compliance issues. Version 3.2.3 was a security update that closes a serious security hole. Version 3.2.4 is a minor bug fix release. All users of Apache Tomcat versions prior to 3.2.3 should updgrade as soon as possible. With the exception of fixes for critical security related bugs, development on the Apache Tomcat 3.2.x branch has stopped.

Apache Tomcat 3.1.x. The 3.1 release contained several improvements over Apache Tomcat 3.0, including servlet reloading, WAR file support and added connectors for the IIS and Netscape web servers. The latest maintenance release, 3.1.1, contained fixes for security problems. There is no active development ongoing for Apache Tomcat 3.1.x. Users of Apache Tomcat 3.1 should update to 3.1.1 to close the security holes and they are strongly encouraged to migrate to the current production release, Apache Tomcat 3.3.

Apache Tomcat 3.0.x. Initial Apache Tomcat release.

We encourage all users to upgrade to Apache Tomcat 5.x whenever possible.