Startup accelerators, also known as Seed accelerators, are fixed-term, cohort-based programs, that include mentorship and educational components and culminate in a public pitch event or demo day. While traditional business incubators are often government-funded, generally take no equity, and rarely provide funding, accelerators can be either privately or publicly funded and cover a wide range of industries. Unlike business incubators, the application process for seed accelerators is open to anyone, but highly competitive. There are specific types of seed accelerators, such as corporate accelerators, which are often subsidiaries or programs of larger corporations that act like seed accelerators.
The main differences between business incubators and accelerators are:
- The application process is open to anyone, but highly competitive. Y Combinator and TechStars have application acceptance rates between 1% and 3%.
- A seed investment in the startups is usually made, in exchange for equity. Typically, the investment is between US$20,000 to US$50,000 in the US, GB£10,000 to GB£50,000 in Europe , or $10,000 to $30,000 in Southeast Asia .
- The focus is on small teams, not on individual founders. Accelerators generally consider that one person is insufficient to handle all the work associated with a startup.
- The startups must "graduate" by a given deadline, typically after 3 months. During this time, they receive intensive mentoring and training, and they are expected to iterate rapidly. Virtually all accelerators end their programs with a "Demo Day", where the startups present to investors.
- Startups are accepted and supported in cohort batches or classes (the accelerator isn't an on-demand resource). The peer support and feedback that the classes provide is an important advantage. If the accelerator doesn't offer a common workspace, the teams will meet periodically.
The primary value to the entrepreneur is derived from the mentoring, connections, and the recognition of being chosen to be a part of the accelerator. The business model is based on generating venture style returns, not rent, or fees for services.
Seed accelerators do not necessarily need to include a physical space, but many do. The process that startups go through in the accelerator can be separated into five distinct phases: awareness, application, program, demo day, and post demo day.
The first seed accelerator was Y Combinator, started in Cambridge, Massachusetts, in 2005, and then later moved to Silicon Valley by Paul Graham. It was followed by TechStars (in 2006), Seedcamp (in 2007), Startupbootcamp (in 2010), Tech Wildcatters (in 2011), several accelerators of SOSV, and Boomtown Boulder (2014).
In Europe, the first accelerator program was started by Accelerace in 2009 in Denmark (strongly subsidised by the Danish government) followed shortly after by Startup Wise Guys in 2012 in Estonia.
With the growing popularity of seed accelerator programs in the US, Europe has seen an increase in accelerators to support a growing startup ecosystem. Top-rated seed accelerator programs in Europe include Seedcamp (based in London), HighTechXL (based in Eindhoven), Startupbootcamp (pan European accelerator with program locations and office spaces based in Copenhagen, Amsterdam, Berlin, Israel, Eindhoven, Istanbul and London) and Startup Wise Guys (Europe's most experienced B2B startup accelerator). 
Forbes published an analysis of startup accelerators in April 2012. Since 2010 there has been substantial growth of Corporate Accelerator programs, which are sponsored by established organizations but follow similar principles.
In 2011 Matthew Clifford and Alice Bentinck, formerly management consultants at McKinsey & Company, co-founded Entrepreneur First, a London-based accelerator which guides promising tech graduates and those already working in technology firms to design and run their own startups. Entrepreneur First differs from other accelerators such as Y Combinator and Wayra in that it works with individuals rather than companies.
With the emergence of the COVID-19 pandemic, many accelerators such as Y Combinator , SOSV's family of accelerators , and BEAMSTART  have shifted their approaches by running most of the programs and Demo Days online.
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