The fourth edition of this work has involved a thorough rewrite. Each chapter has been looked at again from beginning to end, with fresh choices in some cases made for extracts to bring the book up to date for new materials and scholarship and some material rewritten to provide clearer explanation. While all chapters contain changes, some have involved a more fundamental rewrite. The Supplement below, details changes from the 3rd edition to the 4th edition. For example, the chapters on the executive as well as characterisation and the trade and commerce power have been rewritten to provide a more straightforward structure and to provide greater clarity and contemporary relevance. Other changes have been made in order to restructure the book and to provide room for the substantial new material. Overall, the book is roughly the same length as the last edition due to cuts and streamlining. This has also involved rethinking the placement of some material, such as to group together the grants and appropriations powers of the Commonwealth. The material dealing with human rights has been substantially restructured with the chapters dealing with the implied freedom of political communication rewritten to take account of new developments and to provide space for major new cases. The final chapter on constitutional change has also been reworked to include a section dealing on Bill of Rights issues as a contrast to that on the republic.