1) A good web page, by http://welkerswikinomics.com:

The Marshall-Lerner Condition, the J-curve, and the US trade deficit

 

2) A useful video via the same author’s http://www.econclassroom.com:

3) A chance for you to play around with the Marshall Lerner condition yourself:

http://www.eco.rug.nl/~gigengack/ge/ML_Interactive/ML_Interactive.htm