Credit rating of a company or a Institution, made by a specialized agency. In Spain, the lead agency in this field is Fitch Ratings. Levels are: AAA, AA A BBB BB other maximum, but are very bad in general: A bank or big box usually has a rating of AA a bank or medium, a rating of A on 3 March 2008, Fitch has maintained the rating of the city of Barcelona in AA + the rating agencies gave these ratings, or given other namesmore sophisticated, but that, in the end, say the same thing: called: Investment grade MBS representing mortgage prime, that is, those of less risk (would be the AAA, AA and A) Mezzanine, at the intermediate (guess than the BBB and maybe BB) Equity bad, of high risk, i.e. a subprime, which, at this shed, are the protagonists Los investment banks placed easily the best (investment grade)conservative investors, and low interest rates. Other managers of funds, Venture Capital, etc, more aggressive. they wanted more, at all costs, profitability high, among other reasons because these gentlemen come the bonus of year depending on the profitability. Problem: how to sell MBS bad recent managers without that being noticed too that they are incurring excessive risks? 6Th comment: things get complicated and, of course, of the box of savings of San Quirze continue making statements in Expansion happy and content, talking about the good progress of the economy and of Social work they are doing. Some investment banks managed, from the Rating agencies to a re-qualification (a re-rating, Word that does not exist, but it serves to understand us) re-rating is an invention to raise the rating of the bad MBS, which consists of: i. structured in tranches, callers les tranches, ordering, major minor, the probability of default, and with a commitment to prioritize the payment to the less bad.