Goldman Sachs will start with the latest transaction value for Twitter, approximately $10.5 billion, and adjust it up for the improvement in both the overall market and in social media companies (especially Facebook) since the start of the year. They will then create a sales pitch for that value, using the pricing of other social media companies (Facebook and Linkedin, in particular) to argue that Twitter is a bargain at their estimated price. (My guess is that they will focus on the number of users and how Twitter looks like a bargain on that basis.) That sales pitch will be tried out on institutional investors for effect, with the salespersons’ ears especially attuned to either too much enthusiasm from these investors (a sign that the price was set too low) or to little (a signal that it is et too high). The institutional investors, not having a clue about the fair value of Twitter, will talk to each other and ratchet up or down their own enthusiasm based upon what they sense in their compatriots. The investment bank, having tweaked the price based on investor reactions will then do a discounted cash flow valuation, reverse engineered to deliver that price as the final value. (A good test of their valuation skills will be in how well they hide this reverse engineering to make it look like the valuation led to the pricing rather than the other way around). Finally, having learned from the Facebook fiasco that it is better to under price rather than over, they will knock off about 15% off their estimated price/value to set the offering price. At the risk of being hopelessly wrong in hindsight, I would be very surprised if I saw Twitter priced lower than $10 billion or higher than $15 billion, unless there is a major market disturbance- Aswath Damodaran