Hi, I designed component, packaged in jars, using slf4j and logback, this library is then packaged with a third party application using log4j. I presumed that slf4j and logback could be used to change your log system depending on the loaded libraries of your classpath. Here my configuration: my_library.jar using only slf4j and at some point logback dependencies included with it: slf4j-to-log4j.jar slf4j.jar log4j.jar --> already present in the war. logback-*.jar All these libraries are installed into a third part webapp application (client_app.war), directly under the WEB-INF/lib directory of this application. This application has a log4j.properties, in the classes directory, changes are made to create a log4j logger. At my understanding, my library's log events should be redirecting from slf4j/logback to log4j, using the log4j.properties, and so be written in the "client_app..log" configured? Am I wrong? Do I still need a logback.xml to be located under the classes of this webapps as well? Regards, Johan Bos