Here is a list of all related documentation pages:

Backup Design
Books / Accounting Periods
Some Thoughts about GnuCash Budgeting
Business Overview
Financial Constraints in GnuCash
Currency Issues
Useful tips for doxygen in C files
Style discussion
Doxygen reference documentation
Engine Framework
GnuCash Gnome2 architecture
Generic (Import) Druid Framework
gnc_numeric Example
Globally Unique Identifiers: Design Issues
Handling loan repayment in GnuCash::Scheduled Transactions
Lots Architecture & Implementation Overview
Multicurrency Discussion
Price Overview
Python bindings	Also have a look at group Python Bindings Module
QIF importer infrastructure.
Some notes about taxes
User Preferences HOWTO
Engine Architecture (old)
Proposed GnuCash Extensions
KVP Values used By GnuCash
Python invoice export
Todo List
Deprecated List