A demand-side platform (DSP) is a system that allows buyers of digital advertising inventory to manage multiple ad exchange and data exchange accounts through one interface. Real-time bidding for displaying online advertising takes place within the ad exchanges, and by utilizing a DSP, marketers can manage their bids for the banners and the pricing for the data that they are layering on to target their audiences. Much like Paid Search, using DSPs allows users to optimize based on set Key Performance Indicators such as effective Cost per Click (eCPC), and effective Cost per Action (eCPA).
DSPs are unique because they incorporate many of the facets previously offered by advertising networks, such as wide access to inventory and vertical and lateral targeting, with the ability to serve ads, real-time bid on ads, track the ads, and optimize.  This is all kept within one interface which creates a unique opportunity for advertisers to truly control and maximize the impact of their ads. The sophistication of the level of detail that can be tracked by DSPs is increasing, including frequency information, multiple forms of rich media ads, and some video metrics. Many third parties are integrating with DSPs to provide better tracking.
DSPs are commonly used for retargeting, as it is able to see a large volume of inventory in order to recognize an ad call with a user that an advertiser is trying to reach. The percentage of bids that are successfully won over the bids that were submitted is called a win rate.
Demand Side Platforms originally started out by just buying liquid inventory on Real-time bidding Ad exchanges, such as Appnexus, Right Media, PubMatic, AdMeld, Rubicon Project, AdECN by Microsoft, OpenX and Google AdX. 
Types of programmatic buys
- Preferred Deal: No auction, set CPM, non-guaranteed inventory
- Programmatic Guaranteed: No auction, set CPM, guaranteed inventory
- Private Marketplace: Real time bidding, price floor, select group of advertisers
- Open Exchange Buy: Real time bidding, variable cpm, open to all advertisers
- Adobe Media Optimizer (formerly Efficient Frontier)
- DoubleClick Bid Manager (DBM) (originally Invite Media Bid Manager)
- "Top Online Display Demand Side Platforms". Thalamus. Thalamus. Retrieved 12 September 2015.
- "The top five ad exchanges every marketer should be using". Marketing Pilgrim. Marketing Pilgrim. Retrieved 12 September 2015.
||This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. (April 2015)|
- Baker, Mike (2009-12-14). "What Demand-Side Platforms Can Mean for a Media Plan". ClickZ. Retrieved 2011-04-24.
- Dreller, Josh (2010-05-18). "A quick guide to demand-side platforms". iMediaConnection.com. Retrieved 2010-12-29.
- Ebbert, John (2009-08-04). "The Demand-Side, Buying Platform Trend". AdExchanger.com. Retrieved 2011-04-24.
- Graham, Rob (2010-08-25). "The Rise of the Demand Side Platform". ClickZ. Retrieved 2011-04-24.
- Kawaja, Terence. "LUMAscape Display Landscape". LUMAscape. Retrieved 2014-05-05.
- Turner, Nat (2010-02-07). "Not Every Demand-Side Platform (DSP) Is Created Equal: What Is A True DSP?". AdExchanger.com. Retrieved 2011-04-24.
- Rocker, Kj (2015-03-04). "What are Demand Side Platform (DSP) Mobile Networks?". Kj Rocker FZE. Retrieved 2015-06-27.
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