The twenty-four letters of the Greek alphabet are normally transliterated in one of two ways.  Most older texts transform Greek letters into the equivalent in classical Latin, even changing Greek word-endings to better match Latin word-endings. So Greek  κ (kappa) becomes Latin c, and Greek αι (alpha-iota diphthong) becomes Latin ae.  Many newer texts transliterate Greek letters into the equivalent letter in modern English, thus staying closer to the original sound of the word.  So, Greek κ becomes a k, and Greek αι becomes ai. However, modern authors are seldom consistent.  The following table shows the original Greek letters, and the two ways of transliterating them:

Greek Letter Old Method New Method
α a a
αι ae ai
αυ au au
β b b
γ g g
γγ ng ng
γκ gc gk
δ d d
ε e e
ει i ei
ευ eu eu
ζ z z
η e ê
ηυ eu êu
θ th th
ι i i
κ c k
λ l l
μ m m
μπ mp mp
ν n n
ντ nt nt
ξ x x
ο o o
οι oe oi
ον on (um)* on
οσ os (us)* os
u ου
π p p
ρ r r
rh rh
σ/ς s s
τ t t
υ y u
φ ph ph
χ ch kh
ψ ps ps
ω o ô
ων on (o)* ôn
h h

*Forms in parentheses are used at the end of words.