Historical writings on the importance and efficacy of burning joss paper? I was walking through a Taipei grocery/department store a few years ago and saw shelves with packs of "paper money" or joss paper to be used for burning. For the bank-note varieties were three choices; New Taiwan dollars, Chinese RMB, and US dollars. The way different people approach the subject here is quite varied, from very serious to quite light-hearted. 

My question is not really about the origin of the practice as much as it is about its "paper trail". Are there historical buddhist writings that lay out the importance of burning paper money and its efficacy? Or is it more of an unwritten tradition?
It has, like most ritual with material sacrifies, not really a connection to the Buddha-Dhamma, aside of the possible devotion and sacrify, metta and compassion, to ones ancestors, deities or spirits, which are possible wholesome deeds and generally praised by the Buddha (sacrifies for deities and ancestors)

It's a very usual ritual, mostly performed by people with Chinese or Vietnamese ancestors all over SEAsia on Chinese fest days and has it's origin in certain Asian ancestor-cults and religions.

Earlier real money was used which of course is mostly not legal, so copies and fake prints are usually used to be burned in front of the houses.

As a one of a childs "duty" torward death relatives:


  from the Sigalovada Sutta: The Discourse to Sigala - The Layperson's Code of Discipline
  
  "In five ways, young householder, a child should minister to his parents as the East:
  
  (i) Having supported me I shall support them,
  
  (ii) I shall do their duties,
  
  (iii) I shall keep the family tradition,
  
  (iv) I shall make myself worthy of my inheritance,
  
  (v) furthermore I shall offer alms in honor of my departed relatives.[9] 
  
  Note by the translator: 9. This is a sacred custom of the Aryans who never forgot the dead. This tradition is still faithfully observed by the Buddhists of Sri Lanka who make ceremonial offerings of alms to the monks on the eighth day, in the third month, and on each anniversary of the demise of the parents. Merit of these good actions is offered to the departed after such ceremony. Moreover after every punna-kamma (good action), a Buddhist never fails to think of his parents and offer merit. Such is the loyalty and the gratitude shown to parents as advised by the Buddha.
  
  from: Tirokudda Kanda: Hungry Shades Outside the Walls
  
  ...Offerings should be given for the dead
  
  when one reflects thus
  
  on things done in the past.
  
  For no weeping,
  
  no sorrowing
  
  no other lamentation
  
  benefits the dead
  
  whose relatives persist in that way.
  
  But when this offering is given, well-placed in the Sangha,
  
  it works for their long-term benefit
  
  and they profit immediately.
  
  In this way 
  
  the proper duty to relatives has been shown,
  
  great honor has been done to the dead,
  
  and monks have been given strength:
  
  The merit you've acquire
  
  isn't small.


[Note: This is a gift of Dhamma and not meant for commercial purpose or other wordily gains]