Iran has experienced a sharp fertility decline during the late 1980s and 1990s, and reached replacement-level fertility in 2000. However, it is well known that trends in the cross-sectional total fertility rate can be confounded by changes in the timing of births across women's lifetimes (tempo) as well as by changes in the numbers of children that they have by the time they end their childbearing (quantum). Synthetic parity progression ratios provide a much richer interpretation of the trend in period fertility in Iran than does the conventional age-based model. Using the 2000 Iran Demographic and Health Survey (IDHS) and the 2005 Iran Low Fertility Survey, synthetic parity progression ratios are applied to examine the fertility dynamics in Iran during the last two decades. Progressions from marriage to the 1st birth and from the 1st to subsequent births for Iran and the low fertility provinces are presented. The trends of a decomposition of the change in the period lifetime fertility between 1981 and 1999 into changes in the progression to marriage and the progression to each successive birth are also shown. It is observed that there is an emerging trend to delay the first birth following marriage, a longer term trend towards wide spacing between the first and the second birth, and cessation of childbearing after the second birth. Then, based on data relating to four low fertility provinces, the paper examines the contraceptive dynamics associated with the observed changes in parity progression. In particular, contraceptive use before the first birth, in the interval between the first and the second birth and following the cessation of childbearing is analysed. The mix of contraceptive methods varies across the four provinces and by socio-economic characteristics but the fertility outcomes are similar. The paper also examines how the reproductive life span of Iranian women has changed. The paper concludes that, if as expected, the fertility behaviouracross Iran converges to the patterns of delay and limitation observed in the four low fertility provinces, the Total Fertility Rate will continue to fall to levels well below replacement. The implications of these trends for economic and social planning in Iran and for the family planning program are discussed.