: Over time, various professors and students have compiled their own solutions for specific chapters. For instance, a document from the University of Siena

Websites like GitHub and LaTeX repositories often host community-driven solutions. Many PhD students and professors have digitized their handwritten solutions into searchable PDF formats. These are often the most accurate because they are peer-reviewed by the community.

Websites like Chegg or Stack Exchange (Mathematics) host thousands of solved problems from Apostol. While not a cohesive manual, searching by the specific exercise number (e.g., "Apostol Vol 2 Section 2.10 Exercise 5") usually yields a detailed discussion. How to Use a Solution Manual Effectively

While the publisher (Wiley) typically restricts official manuals to instructors, the academic community has developed several high-quality resources over the decades: