This table compares three systems used for transliterating the Greek script into the Latin script.
The ISO 843 transliteration is based on the principles of modern Greek pronunciation. This standard can be obtained from the Central Secretariat, ISO, Case postale 56, 1211 Geneva 20, Switzerland, or purchased from the  ISO website.
The United States Board on Geographic Names/The Permanent Committee on Geographical Names for British Official Use (BGN/PCGN) primarily deals with names of places and people.
The ELOT standard was published in 1976 by the Hellenic Organisation for Standardisation (ELOT), which was set up in 1955 to combat industrial underdevelopment in the wake of the Greek Civil War. This romanization system is now also used by the UN. For more information about the ELOT standard please download this pdf file from www.pcgn.org.uk:  Romanization System for Greek.

GreekISO 843BGN/PCGNUN/ELOT
  α a a a
  β v v v
  γ g g / y* g
  δ d dh/d** d
  ε e e e
  ζ z z z
  η ī i i
  θ th th th
  ι i i i
  κ k k k
  λ l l l
  μ m m m
  ν n n n
  ξ x x x
  ο o o o
  π p p p
  ρ r r r
  σ s s s
  τ t t t
  υ y i y
  φ f f f
  χ ch kh ch
  ψ ps ps ps
  ω ō o o
  αι ai e ai
  αυ au av av, af
  ει ei i ei
  αυ eu ev ev, ef
  ηυ īy iv iv/if
  οι oi i oi
  ου ou u ou
  υι yi i yi
  γγ gg ng ng
  γξ gx nx nx
  γκ gk g, ng gk
  γχ gch nkh nch
  μπ mp b/mb b/mp
  ντ nt d/nd nt

* before αι, ε, ει, η, ι, οι, υ, υι
** between ν and ρ
sometimes doubled between vowels