By Michael Lewis, contributor

Eisman entered finance about the time I exited it. He’d grown up in New York City, gone to yeshiva schools, graduated from the University of Pennsylvania magna cum laude, and then with honors from Harvard Law School. In 1991 he was a thirty-year-old corporate lawyer wondering why he ever thought he’d enjoy being a lawyer. “I hated it,” he says. “I hated being a lawyer. My parents worked as brokers at Oppenheimer securities. They managed to finagle me a job. It’s not pretty but that’s what happened.”

Oppenheimer was among the last of the old-fashioned Wall Street partnerships and survived on the scraps left behind by Goldman Sachs and Morgan Stanley. It felt less like a corporation than a family business. Lillian and Elliot Eisman had been giving financial advice to individual investors on behalf of Oppenheimer since the early 1960s. (Lillian had created their brokerage business inside of Oppenheimer, and Elliot, who had started out as a criminal attorney, had joined her after being spooked once too often by midlevel Mafia clients.) Beloved and respected by colleagues and clients alike, they could hire whomever they pleased. Before rescuing their son from his legal career they’d installed his old nanny on the Oppenheimer trading floor. On his way to reporting to his mother and father, Eisman passed the woman who had once changed his diapers.Oppenheimer had a nepotism rule, however; if Lillian and Elliot wanted to hire their son, they had to pay his salary for the first year, while others determined if he was worth paying at all.

Eisman’s parents, old-fashioned value investors at heart, had always told him that the best way to learn about Wall Street was to work as an equity analyst. He started in equity analysis, working for the people who shaped public opinion about public companies. Oppenheimer employed twenty-five or so analysts, most of whose analysis went ignored by the rest of Wall Street. “The only way to get paid as an analyst at Oppenheimer was being right and making enough noise about it that people noticed it,” says Alice Schroeder, who covered insurance companies for Oppenheimer, moved to Morgan Stanley, and eventually wound up being Warren Buffett’s official biographer. She added, “There was a counterculture element to Oppenheimer. The people at the big firms were all being paid to be consensus.”

Eisman turned out to have a special talent for making noise and breaking with consensus opinion. He started as a junior equity analyst, a helpmate, not expected to offer his own opinions. That changed in December 1991, less than a year into the new job. A subprime mortgage lender called Aames Financial went public, and no one at Oppenheimer particularly cared to express an opinion about it. One of Oppenheimer’s bankers, who hoped to be hired by Aames, stomped around the research department looking for anyone who knew anything about the mortgage business. “I’m a junior analyst and I’m just trying to figure out which end is up,” says Eisman, “but I told him that as a lawyer I’d worked on a deal for The Money Store.” He was promptly appointed the lead analyst for Aames Financial. “What I didn’t tell him was that my job had been to proofread the documents and that I hadn’t understood a word of the fucking things.”

Aames Financial, like The Money Store, belonged to a new category of firms extending loans to cash-strapped Americans, known euphemistically as “specialty finance.” The category did not include Goldman Sachs or J.P. Morgan but did include many little-known companies involved one way or another in the early 1990s boom in subprime mortgage lending. Aames was the first subprime mortgage lender to go public.

The second company for which Eisman was given sole responsibility was called Lomas Financial Corp. Lomas had just emerged from bankruptcy. “I put a sell rating on the thing because it was a piece of shit. I didn’t know that you weren’t supposed to put sell ratings on companies. I thought there were three boxes—buy, hold, sell—and you could pick the one you thought you should.” He was pressured to be a bit more upbeat, but upbeat did not come naturally to Steve Eisman. He could fake upbeat, and sometimes did, but he was happier not bothering. “I could hear him shouting into his phone from down the hall,” says a former colleague. “Joyfully engaged in bashing the stocks of the companies he covered. Whatever he’s thinking, it comes out of his mouth.”

Eisman stuck to his sell rating on Lomas Financial, even after the Lomas Financial Corporation announced that investors needn’t worry about its financial condition, as it had hedged its market risk. “The single greatest line I ever wrote as an analyst,” says Eisman, “was after Lomas said they were hedged.” He recited the line from memory: “‘The Lomas Financial Corporation is a perfectly hedged financial institution: it loses money in every conceivable interest rate environment.’ I enjoyed writing that sentence more than any sentence I ever wrote.” A few months after he published that line, the Lomas Financial Corporation returned to bankruptcy.

By early 2005 Eisman was running his own private equity firm staffed by a group who shared his sense that a great many people working on Wall Street couldn’t possibly understand what they were doing. After going bust in the late 90s, the subprime mortgage machine was up and running again, as if it had never broken down in the first place. If the first act of subprime lending had been freaky, this second act was terrifying. Thirty billion dollars was a big year for subprime lending in the mid-1990s. In 2000 there had been $130 billion in subprime mortgage lending, and 55 billion dollars’ worth of those loans had been repackaged as mortgage bonds. In 2005 there would be $625 billion in subprime mortgage loans, $507 billion of which found its way into mortgage bonds. Half a trillion dollars in subprime mortgage–backed bonds in a single year.

Subprime lending was booming even as interest rates were rising—which made no sense at all. Even more shocking was that the terms of the loans were changing, in ways that increased the likelihood they would go bad. Back in 1996, 65 percent of subprime loans had been fixed-rate, meaning that typical subprime borrowers might be getting screwed, but at least they knew for sure how much they owed each month until they paid off the loan. By 2005, 75 percent of subprime loans were some form of floating-rate, usually fixed for the first two years.

The original cast of subprime financiers had been sunk by the small fraction of the loans they made that they had kept on their books. The market might have learned a simple lesson: Don’t make loans to people who can’t repay them. Instead it learned a complicated one: You can keep on making these loans, just don’t keep them on your books. Make the loans, then sell them off to the fixed income departments of big Wall Street investment banks, which will in turn package them into bonds and sell them to investors. Long Beach Savings was the first existing bank to adopt what was called the “originate and sell” model. This proved such a hit—Wall Street would buy your loans, even if you would not!—that a new company, called B&C mortgage, was founded to do nothing but originate and sell. Lehman Brothers thought that was such a great idea that they bought B&C mortgage. By early 2005 all the big Wall Street investment banks were deep into the subprime game. Bear Stearns, Merrill Lynch, Goldman Sachs, and Morgan Stanley all had what they termed “shelves” for their subprime wares, with strange names like HEAT and SAIL and GSAMP, that made it a bit more difficult for the general audience to see that these subprime bonds were being underwritten by Wall Street’s biggest names.

Eisman and his team had a from-the-ground-up understanding of both the U.S. housing market and Wall Street. They knew most of the subprime lenders—the guys on the ground making the loans. Many were the very same characters who had created the late 1990s debacle. Eisman was predisposed to suspect the worst of whatever Goldman Sachs might be doing with the debts of lower-middle-class Americans. “You have to understand,” he says. “I did subprime first. I lived with the worst first. These guys lied to infinity. What I learned from that experience was that Wall Street didn’t give a shit what it sold.” What he couldn’t understand was who was buying the bonds from this second wave of subprime mortgage lending. “The very first day, we said, ‘There’s going to come a time when we’re going to make a fortune shorting this stuff. It’s going to blow up. We just don’t know how or when.’”

Excerpted from The Big Short: Inside the Doomsday Machine by Michael Lewis. Copyright © 2010 by Michael Lewis. With permission of the publisher, W.W. Norton & Company, Inc.