The most important books I have been involved in are the Works of Pedro Nunes [Obras de Pedro Nunes] in the multi-volume edition published by the Lisbon Academy of Sciences and the Calouste Gulbenkian Foundation (detailed information here). 

Pedro Nunes. 
Obras, 6 vols. 
(Lisboa: Academia das Ciências, Fundação Calouste Gulbenkian, 2002-2012).

This is Vol. V of Pedro Nunes' Works (Nunes' commentary on Peurbach's Theoricae novae planetarum).
See the Projects page for detailed and updated information on the publication of these volumes.
I wrote a short piece for the Boletim da Sociedade Portuguesa de Matemática on this book. See here.

This is a very technical book but filled with interesting and new results by Pedro Nunes. The book's contents had never been studied by historians of science, so the Notes in this volume are all new material.

But I have authored or edited quite a number of other books. See my author's page at Wook.
See below:

Bernardo Jerosch Herold, Thomas Horst, Henrique Leitão (eds.),
História Natural de Portugal de Leonard Thurneysser zum Thurn, ca. 1555-1556
(Lisboa: Academia das Ciências de Lisboa, 2019)
ISBN: 978-972-623-368-8, 129 pp. [free download here]

A. J. Barros Veloso (coord.), A. J. Barros Veloso, Luiz Damas Mora, Henrique Leitão (eds.),
Médicos e Sociedade. Para uma História da Medicina em Portugal no século XX
(Lisboa: By the Book, 2017).
863 pp. ISBN: 978-989-8614-56-8

A piece about the book, by Maria João Avillez, here.

Thomas Horst, Marília dos Santos Lopes, Henrique Leitão (eds).,
Renaissance Craftsmen and Humanistic Scholars. Circulation of Knowledge between Portugal and Germany
(Frankfurt am Main: Peter Lang, 2017). 
245 pp. ISBN: 978-3-631-68113-8.

More information about the book and online orders: here.

Luana Giurgevich e Henrique Leitão,
Clavis Bibliothecarum: Catálogos e Inventários de Livrarias de Instituições Religiosas em Portugal até 1834
(Lisboa: Secretariado Nacional para os Bens Culturais da Igreja, 2016). 
lxx + 863 pp. ISBN: 978-989-97257-0-6.

There is a Blog (in Portuguese) and a Site (in English) about the book.
More information about the book, Table of Contents, and online orders: here.
This book was awarded a "Menção Honrosa" of the Prize "Lusitania - História", Academia Portuguesa da História, 2016.

Francisco Malta Romeiras and Henrique Leitão, eds.
Obra Selecta do P. Luís Archer, S. J.
4 vols. (Lisboa: Fundação Calouste Gulbenkian, 2015-17).
ISBN: 978-972-31-1566-6.
vol. I: História e Filosofia da Ciência; 474 pp.  
vol. II: Ciência e Religião; 342 pp.
vol. III: Bioética, 1980-1997; 403 pp.
vol. IV: Bioética, 1998-2007; 499 pp.

Selected works of the celebrated geneticist and expert in bioethics. 

Henrique Leitão,
Savants ou artisans, à qui doit-on la modernité scientifique?
(Paris: Fondation Calouste Gulbenkian - délégation en France, 2016).
ISBN: 978-972-8462-89-5.

Bernardo Mota and Henrique Leitão, 
Francisco de Melo: Obras Matemáticas
[vol. I: Texto Latino e Tradução] 
(Lisboa: Centro de Estudos Clássicos e Biblioteca Nacional de Portugal, 2014).
506 pp. ISBN: 978-972-9376-31-3.

Samuel Gessner published an extended Review of our book in Historia Mathematica, 45 (2018) 182-185

The book is fully downloadable at the Repositório da Universidade de Lisboa.

Henrique Leitão, ed.
360º Ciência Descoberta.
(Lisboa: Fundação Calouste Gulbenkian, 2013).
127 pp. ISBN: 978-972-99098-6-3.

The Catalogue of an exhibition at the Calouste Gulbenkian Foundation on Portuguese and Spanish science in the 15th-16th centuries.

Henrique Leitão e José Eduardo Franco (orgs)
Jesuítas, Ciência e Cultura no Portugal Moderno.
Obra Selecta do Pe. João Pereira Gomes SJ.
(Lisboa: Esfera do Caos, 2012)
349 pp. ISBN: 978-989-680-059-8.

João Pereira Gomes SJ, was a remarkable historian. Despite a short productive period, he left a number of contributions of great value, especially related to Jesuit culture and education. This book collects some of his most important works.

Galileu Galilei. 
Sidereus Nuncius. O Mensageiro das Estrelas
Tradução, Estudo e Notas por Henrique Leitão
(Lisboa: Fundação Calouste Gulbenkian, 2010)
286 pp. ISBN: 978-972-31-1317-4.    

First translation in Portugal of Galileo's epoch-making Sidereus Nuncius. Actually, first translation ever in Portugal of a complete book by Galileo. The publication of this book generated lots of media attention both before and after its official presentation to the public on March 17, 2010. Newspaper Público made a piece in it (Ana Machado, «Portugal esperou 400 anos pela tradução de uma obra de Galileu»), ionline, Diário de Notícias, Ciência Hoje also had some information, as well as some blogs (See here, here, and here). I had a long interview on the radio (Antena 2) with journalist Paulo Guerra and collaborated in a public presentation of the book in Coimbra (some images here). See also the nice and detailed review, by Emma Sallent Del Colombo (in Actes d'Història de la Ciència i de la Tècnica, 3 (2010) 95-97). 

The book can be ordered at the Calouste Gulbenkian Foundation.

Henrique Leitão (texto) e Jorge Miguel (ilustrações)
Chamo-me ... Pedro Nunes 
(Lisboa: Didáctica Editora, 2010)
64 pp. ISBN: 978-972-650-843-4.

The story of the life and scientific accomplishments of Pedro Nunes, for young readers. This was my first attempt at writing for a very young audience. I am somewhat curious to see if I succeeded or not. It was much harder than I had anticipated; can you imagine trying to interest young readers in the life of a sixteenth century mathematician? Not easy... The illustrations are by Jorge Miguel, a very talented illustrator I was fortunate to work with.Falta apagar o lápis is his blog. There are no contemporary representations of Pedro Nunes. We haven't the faintest idea of his physical appearance. This was an extra difficulty we had to cope with. 

The book can be ordered directly at the site of Didáctica Editora.

Henrique Leitão,
Os Descobrimentos Portugueses e a Ciência Europeia
(Lisboa: Alêtheia, Fundação Champallimaud, 2009)
104 pp. ISBN: 978-989-622-196-6.

A brief summary of the fifteenth and sixteenth century Portuguese scientific activities. Beautiful pictures. I wrote a text trying to provide a nice overview, with reference to some of the most recent research. 

The book can be ordered here or here.

Manuel Bocarro. Tratado dos Cometas que Apareceram em Novembro Passado de 1618. 
Henrique Leitão (Lisboa: Biblioteca Nacional, 2009)
20 f. ISBN: 978-972-565-443-9.

Manuel Bocarro's Tratado dos Cometas is one of the most interesting Portuguese scientific books of the seventeenth century. Fully downloadable here.

Estrelas de Papel. Livros de Astronomia dos séculos XIV a XVIII
Comissário científico: Henrique de Sousa Leitão; coordenação técnica: Lígia de Azevedo Martins 
(Lisboa: Biblioteca Nacional de Portugal, 2009)
197 pp. ISBN: 978-972-565-442-2.    

Catalogue of the Exhibition at the National Library.

Orders to Biblioteca Nacional de Portugal.

Sphaera Mundi: A Ciência na «Aula da Esfera». Manuscritos Científicos do Colégio de Santo Antão nas colecções da BNP.  Comissário científico: Henrique de Sousa Leitão; coordenação técnica: Lígia de Azevedo Martins 
(Lisboa: Biblioteca Nacional de Portugal, 2008)
247 pp. ISBN: 978-972-565-426-2.

More information about this book here.

Book can be fully downloaded here [pdf - 7.6MB]. Book can be ordered here.

Henrique Leitão, 
A Ciência na “Aula da Esfera” no Colégio de Santo Antão, 1590-1759 
(Lisboa: Comissariado Geral das Comemorações do V Centenário do Nascimento de S. Francisco Xavier, 2007) 110 pp. 

Unfortunately, not easy to find. It can ordered to livraria Alêtheia (R. do Século, 13) or Revista Brotéria (R. Maestro António Taborda, 14, Lisboa).

Conceição Tavares e Henrique Leitão, 
Bibliografia de História da Ciência em Portugal, 2000-2004 
(Lisboa: Centro de História das Ciências da Universidade de Lisboa, 2006)
132 pp. ISBN: 989-95044-0-8. 

The book can be fully downloaded here.

There is also an Adenda & Corrigenda

Luís Saraiva and Henrique Leitão (eds.), The Practice of Mathematics in Portugal. Papers from the International Meeting organized by the Portuguese Mathematical Society, Óbidos, 16-18 November, 2000 (Coimbra: Acta Universitatis Conimbrigensis, 2004)
758 pp. ISBN: 972-8704-38-0. 

Proceedings of an International meeting on the History of Mathematics in Portugal. The book can be ordered at Wook, or at Livraria Almedina or at the Imprensa da Universidade de Coimbra.

O Livro Científico Antigo dos séculos XV e XVI. Ciências físico-matemáticas na Biblioteca Nacional. Catálogo de livros científicos dos séculos XV e XVI. Comissário científico: Henrique de Sousa Leitão; coordenação técnica: Lígia de Azevedo Martins
(Lisboa: Biblioteca Nacional, 2004)
536 pp. ISBN: 972-565-384-X.

This is the Catalogue of scientific books of the fifteenth and sixteenth centuries at the National Library in Portugal. I am working on the catalogue for the seventeenth century, but it will take a while.

This book can be ordered contacting the Biblioteca Nacional de Portugal, and it is partially avaible via Google Books.

Luís Trabucho de Campos, Henrique Leitão and João Filipe Queiró (eds.), 
International Conference: Petri Nonii Salaciensis Opera, Lisbon-Coimbra, 24-25 May 2002. Proceedings 
(Lisboa: Departamento de Matemática, Faculdade de Ciências da Universidade de Lisboa, 2003)
184 pp. ISBN: 972-8394-17-9. 

Proceedings of an International Conference on Pedro Nunes held in 2002. A collection of papers by some leading scholars.

Unfortunately, not easy to find. It was published by the Departamento de Matemática da Universidade de Lisboa. Try contacting them. (If you are really desperate to get the book and cannot find it, send me a message).

Pedro Nunes, 1502-1578: Novas terras, novos mares e o que mays he: novo ceo e novas estrellas
Catálogo bibliográfico sobre Pedro Nunes. Comissário científico: Henrique de Sousa Leitão; coordenação técnica: Lígia de Azevedo Martins 
(Lisboa: Biblioteca Nacional, 2002)
304 pp. ISBN: 972-565-339-4.

Bibliographical catalogue about Pedro Nunes. Here can be found the most exhaustive and detailed bibliographic description not only of Pedro Nunes' own works, but also of many other relayed books. Both his sources and the books that cite him are presented and described. Besides the catalogue itself, this book has some studies.
This book can be ordered contacting the Biblioteca Nacional de Portugal, and it is partially avaible via GoogleBooks.

Henrique de Sousa Leitão, 
O Comentário de Pedro Nunes à Navegação a Remos 
(Lisboa: Edições Culturais da Marinha, 2002) 
104 pp. ISBN: 972-8004-54-0.

Translation and study of an important work by Pedro Nunes (1502-1578) on the mechanical problem of rowing. It is the first study of this work by the famous Portuguese sixteenth century mathematician.
Nunes' mathematical commentary on the problem of rowing is the first major step forward in the understanding of this problem after (pseudo-) Aristotle's highly qualitative analysis in Mechanical Questions, and the most interesting discussion until Euler's contributions.

The book was published by the Comissão Cultural de Marinha and can be ordered contacting them.

Together with Ana Simões, I coordinated the Colecção História e Filosofia da Ciência, published by Porto Editora (14 vols. were published):

    1. Helge Kragh, Introdução à Historiografia da Ciência (2003);
    2. Richard S. Westfall, A Construção da Ciência Moderna. Mecanismos e Mecânica (2003);
    3. George Basalla, A Evolução da Tecnologia (2004);
    4. Edward Grant, Os Fundamentos da Ciência Moderna na Idade Média (2004);
    5. Thomas L. Hankins, Ciência e Iluminismo (2004);
    6. Alan Debus, O Homem e a Natureza no Renascimento (2004);
    7. John Hedley Brooke, Ciência e Religião. Algumas perspectivas históricas (2005);
    8. Mario Biagioli, Galileu, Cortesão. A Prática da Ciência na Cultura do Absolutismo (2006).
    9. Yves Gingras, Peter Keating e Camille Limoges, Do Escriba ao Sábio. Os detentores do Saber da Antiguidade à Revolução Industrial (2007);
    10. Ana Simões, Maria Paula Diogo, Ana Carneiro, Cidadão do Mundo. Uma biografia científica do abade Correia da Serra (2006);
    11. Kostas Gavroglu, O Passado das Ciências como História (2007);
    12. Michael Sharrat, Galileu, Inovador (2010).
    13. Thomas S. Kuhn, O Percurso desde A Estrutura (2011).
    14. Robert E. Kohler, Os Senhores da Mosca. A genética da Drosophila e a Vida Experimental (2011).