This revised and expanded edition of Ralph Penny's authoritative text includes new material on the nature of linguistic history, the concept of World Spanish, processes of convergence and divergence in Spanish and the English/Spanish interface. This edition also contains a glossary of technical terms, guidance on further reading and suggested topics for discussion.
Pretty approachable as long as you have a decent grasp of phonetic terminology. I'm sure a Spanish historical grammar would be very interesting to someone with better knowledge of either Latin or another modern Romance language. I'll be coming back to the section on the development of the verb once my understanding of the modern Spanish verb is better.
This is a high 3-star as it does everything it says on the back cover, it just didn't necessarily 'wow' me the way some exceptional textbooks have.