Japan intervened in currency markets on Thursday to curb the yen's gains that officials fear threatened to derail the economy's recovery from a slump triggered by a massive earthquake in March.
Here are some milestones in the yen's 140-year history:
1871 - The yen becomes Japan's currency as part of the Meiji Restoration, which marked the start of Japan's modernisation and opening to the rest of the world. Japan adopts the gold standard.
1949 - After World War Two the US dollar's fixed rate is set at 360 yen via the Bretton Woods system, partly to help stabilise prices in the Japanese economy.
1959 - The US dollar/yen exchange rate is liberalised. The margin of fluctuation is set at 0.5 per cent on either side of its US dollar parity.
1963 - The margin of fluctuation is widened to 0.75 per cent.
1971 - The United States abandons the gold standard. The end of the Bretton Woods system of fixed exchange rates forces a realignment of world currencies.
Dec. 1971 - The Smithsonian Agreement sets the US dollar/yen exchange rate at 308 yen, and allows it to fluctuate in a wider band between 301.07 yen and 314.93 yen.
1973 - Japanese monetary authorities decide to let the yen float freely against the greenback, and it appreciates as far as 263 to the US dollar.
1978 - The yen pushes through 200 to the US dollar for the first time, strengthening as far as 177.
1980 to 1985 - The yen's appreciation halts and partially reverses despite Japan's big trade surpluses. Higher U.S. interest rates see Japanese investors put money in US dollar assets.
1985 - The Group of Five industrial nations, the predecessor to the G7, sign the Plaza Accord in which they agree that the US dollar is overvalued and that they will move to weaken it. The yen climbs from its pre-accord level around 240 to 211 in October and 200 in November, a 20 per cent rise in just a few months.
1986 - The U.S. currency falls further to around 190 yen in January, 167 yen in April and 153 yen in August.
1987 - In February, six of the G7 nations sign the Louvre Accord, which aims to stabilise currencies and halt the US dollar's broad decline. The US dollar still falls from near 153 to 137 in April and 120.80 by the end of the year.
1988 - On Jan. 4, the US dollar falls to a post-war low of 120.45 yen in Tokyo trade, a level that holds as the low for more than five years. The Bank of Japan intervenes to buy US dollars and sell yen that day on behalf of the Ministry of Finance.
Aug. 17, 1993 - The US dollar declines to a new post-war low of 100.40 yen in Tokyo.
June 21, 1994 - The US dollar falls through the key 100 yen level and touches a record postwar trough of 99.85 yen in New York trade before finishing at 100.30 yen.
April 19, 1995 - The US dollar hits a record postwar low at 79.75 yen after U.S.-Japanese trade frictions spark heavy selling. By the end of the year it is near 103.40.
1998 - The Asian financial crisis sees the yen weaken to nearly 148 to the US dollar in August, even after U.S. authorities join the Bank of Japan to buy yen, spending $833 million, in June.
In October, US dollar tumbles from near 136 yen to 111.50 yen, as carry trades unwind following the near-collapse of hedge fund major Long-Term Capital Management.
1999 - The yen strengthens further despite repeated intervention, reaching 102 in November.
2001 - Following the Sept 11 attacks on the United States, the Bank of Japan intervenes to sell yen for US dollars.
2003 - The Ministry of Finance begins massive intervention to halt the yen's rise against the US dollar, partly to shield Japanese exporters as the economy remains stuck in its post-bubble slump and deflation. The MOF spends 20.4 trillion yen ($200 billion) over the year, nearly all of it to buy US dollars and sell yen.
2004 - The MOF spends 14.8 trillion yen ($145 billion)intervening in the first quarter of the year, including 1.67 trillion yen buying US dollars on Jan. 9 alone.
2005 - The yen hits a high of 101.67 yen in January but then falls, marking 121.40 in December. Yen carry trades and Japanese investors shifting funds into foreign assets drive the slide.
June 2007 - The US dollar hits a 4-1/2 year high of 124.14 yen.
July 2007 - Yen's broad depreciation takes it to a 22-year low on a real effective exchange rate (REER) basis. Since January 2005 the yen loses 25 per cent of its value on a REER basis.
October 2008 - Yen hits 13-year high of 90.87 vs the US dollar, with its surge prompting the G7 to issue a statement singling out the yen in warning on currency market volatility.
December 2008 - The US dollar falls through 90 yen for the first time in 13 years after a bill to rescue U.S. automakers fails in the Senate.
September 2009 - Marks 8-month high of 88.23 against greenback, but later loses ground as Japan's finance minister tries to tone down earlier comments suggesting intervention was unlikely.
October, 2009 - Yen reaches fresh 8-month high versus the greenback of 88.01 as market players probe how far Japanese authorities will allow the yen to rise.
Nov. 27, 2009 - Hits 14-year high of 84.82 on trading platform EBS.
Sept. 15, 2010 - Japan intervenes in the currency market for the first time in six years, selling yen to stem a rise in the currency after the US dollar hits a 15-year-low at 82.87 yen.
March 18, 2011 - G7 nations jointly intervene to stem yen strength when the currency spikes to a record high of 76.25 to the US dollar in the aftermath of a massive earthquake, on speculation that Japanese firms would repatriate some of their huge foreign assets to pay for reconstruction
Aug. 1 - The yen trades as high as 76.29 per US dollar on EBS, close to its record peak in March, fanning speculation that authorities could step into the market.
Aug. 4 - Japan intervenes to curb the yen's gains that officials fear threaten to derail the economy's recovery from a slump triggered by March's quake. Finance Minister Yoshihiko Noda says Japan acted alone.
Sources: Reuters, Bank of Japan, Bank of England