A wide variety of acoustic tools is available to assess the properties of wood but only Time of Flight (TOP) tools provide a way of assessing the properties of standing trees. The objective of this study is threefold: to test for factors that could have an influence on the acoustic properties in trees, such as tree height, compression wood or stocking (Chapter 3); to test TOP tools for their suitability in the field to assess standing trees (Chapter 2, 4 and Appendices I to III); and to gain an insight into how the acoustic properties of outerwood relate to those of corewood and lumber (Chapter 4). Standing trees of different ages and stockings are assessed with the Fakopp 2D (Chapter 3). Further studies are conducted in the laboratory with a variety of acoustic tools on lumber and logs (Chapter 2, 4 and Appendix I to III). Statistical analyses with t-Tests and regressions test for conelations between acoustic velocity and other factors (Chapter 3). Further, statistical tests are used to test for correlations amongst these TOP tools and with the resonance tool WoodSpec (Chapter 2 and 4). There are no correlations between the acoustic velocity of trees and stocking, tree height or diameter. There are possible correlations between acoustic velocity and tree age, knots and compression wood respectively but this requires further study (Chapter 3 and 4). In addition, the differences in velocity between geographical regions are found to be significant (Chapter 3). Strong correlations are found between TreeTap and Fakopp 2D, which also show good correlations with WoodSpec (Chapter 2 and 4). Furthermore, correlations are found between the acoustic velocity of outerwood and corewood, thus demonstrate that it is possible to predict corewood properties from stemwood properties using TOP tools. This result reinforces the concept of developed within-log stiffness maps (Chapter 3). The results gained using TOP tools on logs, correlate well with those determined on green and air-d1y lumber (Chapter 4). Exposure to prevailing winds and a long term trial for stiffness maps of trees are identified as the main topics for future research (Chapter 5).