At the time he wrote this book, his last, Prof. Weinberg was generally considered the greatest living theoretical physicist, and rightly so.  At a time when most people his age are far into retirement, he was--- as seen here --- delighting in getting to re-do derivations by the likes of Einstein and Fermi, and making them stronger and more general.  However, we need some background as to what the term "modern physics" means in physics education.  At the end of the 2nd World War, 1945, as physicists and physics students returned to the universities, textbooks had to be written to cover the developments in physics from 1905 to the late 1940s or early 1950s.  These books were titled "Modern Physics," although "20th Century Physics" would have been a far more accurate label.  Typically they covered special relativity (1905), the pre-quantum era (1910 - 20), were alas very thin with genuine quantum physics (1925), ignored quantum field theory (1930s)--- the actual most important development of the century--- and sketched out aspects of atomic, molecular, solid-state, nuclear (1930s) and the very beginnings (1950s) of particle physics.  Today the texts are not very different, so that "modern physics" now refers to  physics roughly a century old!!<br><br>What Weinberg did here is to write a text that goes over in great detail the most important developments from the last few decades of the 19th Century, up until the development and applications of quantum field theory.  The level of sophistication and complexity of detail is often nearly overwhelming, and as a result the book doesn't fit into the spectrum of classes that a student might take in his or her last two years of undergraduate work, or beginning graduate work.  Specifically, Weinberg covers early thinking about an atomic description of matter, the development of thermodynamics and kinetic theory of gases, the beginnings of quantum ideas, special relativity, actual quantum physics (circa 1925), nuclear physics, and relativistic quantum field theory!  Weinberg's notation, as usual in his physics monographs, is often very nonstandard, so that his important quantities are so loaded with huge numbers of superscripts and subscripts that the fonts dwindle to microscopic levels that were a great challenge to my elderly eyesight.<br><br>As another example, he avoids the universally-adopted bra-ket formulation of state vectors in Hilbert space, replacing it by a very clumsy and inelegant mess... it's as if he didn't have certain mathematical symbols available on his computer. The level of mathematical sophistication is enormously high, far beyond what the normal physics undergraduate student sees even at a very good university.  I can almost hear Weinberg chuckling--- he was my colleague here at UT Austin for many decades--- as he sets up and tackles an integral that would send deep terror into the soul of anyone who is not supremely mathematically talented.  The book has almost no diagrams, but they would certainly have helped students in comprehending how to do the many contour integrals that are encountered.<br><br>I think the best audience for this thoughtful and insight-filled volume is professional physicists.  Let a master show you the details you didn't get in either your undergraduate or graduate physics education.  He has many very deep thoughts to share with readers, within nearly every topic he presents.