Cover letter v/s statement of research interests I saw a postdoctoral position advertisement in engineering field, which has asked applicants to submit a cover letter  and a statement of research interest. If these two are not explicitly asked, then I usually prepare single document mostly containing my research interest along with a CV.

I would like to know what should be the content of the two different documents, means what should go where?

Thanks
Statement of research interest seems to deal specifically with you potential future research. Though, you can obviously base your future project describing your proved past record. The cover letter seems to be a general info, something that you are XYZ  who completer PhD in ABC university, has the following background and you are interested in this position. In the cover letter I would briefly mention your research interests and refer for more details to the  statement of research interest. 

I think that there is nothing special about this two-letters format, but it is just some bureaucratic requirement of the university.  May be worth asking them  how long should be research statement - because you can potentially write one page or 15 pages like a full grant.