Although not clearly defined, the backlog of unexamined patent applications consists, at one point in time, of all the patent applications that have been filed and still remain to be examined. The backlog was said to be 4.2 million worldwide in 2007, and as of 2009 it reportedly continues to grow. Alone, the United States Patent and Trademark Office (USPTO) is reported to have, as of 2009, a backlog of more than 700,000 patent applications. According to Beth Simone Noveck,
According to Alison Brimelow, president of the European Patent Office as of 2009, the "backlog of patent applications is counter-productive to legal certainty, and that has a negative effect on the innovation process". According to a 2010 study by London Economics, "the cost to the global economy of the delay in processing patent applications may be as much as £7.65 billion each year."
According to former U.S. federal judge Paul R. Michel, in an interview conducted in 2011, "delay is [...] the greatest problem with the [U.S.] patent system" and "[the USPTO] desperately needs thousands of additional examiners and new IT systems. Indeed, it has needed them for years."
Since 2006, a number of collaborations, known as Patent Prosecution Highway (PPH), have been set up between various patent offices, in order to avoid the duplication of search and examination work and ultimately reducing the patent backlog.
While politicians are keen to reduce patent backlogs, those applying for patents can often prefer a lengthy 'patent pending' period. The delay can benefit the applicant by (i) deferring costs associated with examination and grant; (ii) deferring decisions regarding amendments to the application; and (iii) maintaining uncertainty for competitors as to what scope of protection may eventually be granted.