Geotechnical Aspects of Underground Construction in Soft Ground comprises the second Fujita lecture, three keynote lectures and the regular papers presented at the Ninth International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground (IS - Sao Paulo 2017, Sao Paulo, Brazil, 4-6 April 2017). The Symposium was organized by the Brazilian Tunnelling Committee (CBT) of the Brazilian Geotechnical Society (ABMS), under the auspices of the Technical Committee TC204 of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). The contributions cover a wide range of topics: - Deep Excavations - Interaction with Adjacent Structures - Mechanized Excavations - Sequential Excavations - Physical Modelling and Field Tests - Case Histories Geotechnical Aspects of Underground Construction in Soft Ground is particularly aimed at academics and professionals interested or involved in geotechnical and underground engineering. Similarly to previous editions, the contributions are a valuable source of reference on the current practice on the analysis, design and construction of tunnels, deep excavations and large underground structures, with particular emphasis on the development, effects and control of ground movements, their interaction with existing structures, mitigation measures and risk management. IS - Sao Paulo 2017 is the latest in a series of ISSMGE's TC204 symposia, which began in New Delhi (1993), followed by symposia in London (1996), Tokyo (1999), Toulouse (2002), Amsterdam (2005), Shanghai (2008), Rome (2011) and Seoul (2014).