The most cited paper published by GEOPHYSICS, according to the ISI Web of Knowledge (operated by Thomson Reuters), is Leon Thomsen's 1986 article “Weak elastic anisotropy.” This paper, which introduced the now standard Thomsen anisotropic parameters, had been cited more than 780 times at the time this anniversary issue of GEOPHYSICS was going to press. A statistician looking at this number might reject it as an outlier because it is far more than any other paper published by GEOPHYSICS in its 75 year history. The paper with the second highest number of citations (628) was “Occam's inversion — a practical algorithm for generating smooth models from electromagnetic sounding data” by S. C. Constable, R. L. Parker, and C. G. Constable, published in 1987. The difference in number of references to the top two papers, more than 150, is striking as the two papers at numbers 49 and 50 had been cited 185 and 184 times, respectively. Thomsen's paper is also, of course, the most cited article published by GEOPHYSICS in the last 25 years and comparison with others in this category puts the importance of this work into even starker relief. It has been cited nearly 600 more times than the 16th paper on that list, “Velocity analysis for transversely isotropic media” by T. Alkhalifah and I. Tsvankin (which is an extension of Thomsen's work and, of course, cites it). This paper is also 47th on the “all years” list. Chris Liner, former editor of GEOPHYSICS (1999–2001), gave a concise analysis of the importance of Thomsen's breakthrough in World Oil in July 2010: A bit more about anisotropy is in order. The tendency of seismic waves to have directional velocity was well known 50 years ago, and the theory was worked out in detail 50 years before that. But anisotropy …