An Introduction to Formal Logic was first published by Cambridge University Press in November 2003 (with later corrected reprintings). This is an accessible quite slow-paced introductory textbook aimed at beginning philosophy students.
I am now working on a second edition, at the suggestion of CUP, hopefully to be published by them in due course.
The planned major difference between the editions will be that, while the first edition is ‘logic by trees’, the second edition will also have some chapters on natural deduction (Fitch-style as students find that easier than Gentzen-style).
Here is a web-page for the first edition, saying more about the book, linking to answers to exercises, and including some other materials. There are also lists of corrections for the various printings.
The second edition is being re-written throughout, with some significant changes quite apart from the promised new material on ND. Hopefully, the book will be even more accessible, partly because I plan to omit some of the fancier content in later chapters of the first edition (which will then become available on supplementary web pages).
As a taster, here is a draft of the first ten chapters of the second edition. (Do note the ‘Notes to readers’ at the very beginning!)