Arctic sea ice has been noted to be in decline throughout the era of satellite observations. This decline was especially steep between 1995 and 2012, although the rate of decline has decreased considerably since then. The reconstructed state-space projection in two dimensions of Arctic sea ice extent by summer minima shows clear evidence of multistability, with a greater-ice-extent state (noted in data from 1972 until about 2000), followed by a period of rapid change toward a stable lower-ice-extent state (since about 2008). These different states represent regions of stability in state space and are related to the internal dynamics of the climate system. The rapid decline of minimum Arctic sea-ice extent observed between 1995 and 2012 was due to this change in state. A similar change in state is observed in the proxy for summer ice-melt used in this chapter, being the difference in areal extent between the winter maximum and late-summer minimum, which occurs after 2000. This suggests that a sudden intensification of summer melting since 2000 may be the principal mechanism of the observed reduction in Arctic sea-ice extent. The existing record is too short to determine the full variability in the sea-ice system, complicating attempts to forecast the future for Arctic sea ice.