diff --git a/.gitignore b/.gitignore
index 369ae03..9df679a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,4 @@ deps/build.log
 *.jl.mem
 Manifest.toml
 .vscode
+test/write_tests/
\ No newline at end of file
diff --git a/Project.toml b/Project.toml
index 761d41d..6ac772b 100644
--- a/Project.toml
+++ b/Project.toml
@@ -3,17 +3,18 @@ uuid = "d71aba96-b539-5138-91ee-935c3ee1374c"
 version = "1.1.2-DEV"
 
 [deps]
-Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
 DataValues = "e7dc6d0d-1eca-5fa6-8ad6-5aecde8b7ea5"
+Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"
 ReadStat_jll = "a4dc8951-f1cc-5499-9034-9ec1c3e64557"
-
-[extras]
-Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+Tables = "bd369af6-aec1-5ad0-b16a-f7cc5008161c"
 
 [compat]
-julia = "1.3"
 DataValues = "0.4.13"
 ReadStat_jll = "1.1.1"
+julia = "1.3"
+
+[extras]
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
 test = ["Test"]
diff --git a/src/C_interface.jl b/src/C_interface.jl
index 4880bcd..c486ff9 100644
--- a/src/C_interface.jl
+++ b/src/C_interface.jl
@@ -20,7 +20,7 @@ function readstat_get_var_count(metadata::Ptr{Nothing})
 end
 
 function readstat_value_is_missing(value::ReadStatValue, variable::Ptr{Nothing})
-    return Bool(ccall((:readstat_value_is_missing, libreadstat), Cint, (ReadStatValue,Ptr{Nothing}), value, variable))
+    return Bool(ccall((:readstat_value_is_missing, libreadstat), Cint, (ReadStatValue, Ptr{Nothing}), value, variable))
 end
 
 function readstat_variable_get_index(variable::Ptr{Nothing})
@@ -78,3 +78,64 @@ end
 function readstat_variable_get_missing_ranges_count(variable::Ptr{Nothing})
     return ccall((:readstat_variable_get_missing_ranges_count, libreadstat), Cint, (Ptr{Nothing},), variable)
 end
+
+
+function readstat_begin_row(writer)
+    return ccall((:readstat_begin_row, libreadstat), Int, (Ptr{Nothing},), writer)
+end
+
+function readstat_end_row(writer)
+    return ccall((:readstat_end_row, libreadstat), Int, (Ptr{Nothing},), writer)
+end
+
+function readstat_begin_writing(writer, filetype::Val{:dta}, io, row_count)
+    return ccall((:readstat_begin_writing_dta, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cint), writer, pointer_from_objref(io), Cint(row_count))
+end
+
+function readstat_begin_writing(writer, filetype::Val{:sav}, io, row_count)
+    return ccall((:readstat_begin_writing_sav, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cint), writer, pointer_from_objref(io), Cint(row_count))
+end
+
+function readstat_begin_writing(writer, filetype::Val{:por}, io, row_count)
+    return ccall((:readstat_begin_writing_por, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cint), writer, pointer_from_objref(io), Cint(row_count))
+end
+
+function readstat_begin_writing(writer, filetype::Val{:sas7bdat}, io, row_count)
+    return ccall((:readstat_begin_writing_sas7bdat, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cint), writer, pointer_from_objref(io), Cint(row_count))
+end
+
+function readstat_begin_writing(writer, filetype::Val{:xport}, io, row_count)
+    return ccall((:readstat_begin_writing_xport, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cint), writer, pointer_from_objref(io), Cint(row_count))
+end
+
+function readstat_insert_double_value(writer, variable, value)
+    return ccall((:readstat_insert_double_value, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cdouble), writer, variable, value)
+end
+
+function readstat_insert_float_value(writer, variable, value)
+    return ccall((:readstat_insert_float_value, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cfloat), writer, variable, value)
+end
+
+function readstat_insert_int32_value(writer, variable, value)
+    return ccall((:readstat_insert_int32_value, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cint), writer, variable, value)
+end
+
+function readstat_insert_int16_value(writer, variable, value)
+    return ccall((:readstat_insert_int16_value, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cshort), writer, variable, value)
+end
+
+function readstat_insert_int8_value(writer, variable, value)
+    return ccall((:readstat_insert_int8_value, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cchar), writer, variable, value)
+end
+
+function readstat_insert_string_value(writer, variable, value)
+    return ccall((:readstat_insert_string_value, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}, Cstring), writer, variable, value)
+end
+
+function readstat_insert_missing_value(writer, variable)
+    return ccall((:readstat_insert_missing_value, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}), writer, variable)
+end
+
+function readstat_add_variable(writer, name, type, width)
+    return ccall((:readstat_add_variable, libreadstat), Ptr{Nothing}, (Ptr{Nothing}, Cstring, Cint, Cint), writer, name, type, width)
+end
\ No newline at end of file
diff --git a/src/ReadStat.jl b/src/ReadStat.jl
index a0e5e1e..5de462a 100644
--- a/src/ReadStat.jl
+++ b/src/ReadStat.jl
@@ -11,8 +11,9 @@ using ReadStat_jll
 using DataValues: DataValueVector
 import DataValues
 using Dates
+import Tables
 
-export ReadStatDataFrame, read_dta, read_sav, read_por, read_sas7bdat, read_xport
+export ReadStatDataFrame, read_dta, read_sav, read_por, read_sas7bdat, read_xport, write_dta, write_sav, write_por, write_sas7bdat, write_xport
 
 ##############################################################################
 ##
@@ -287,10 +288,96 @@ function parse_data_file!(ds::ReadStatDataFrame, parser::Ptr{Nothing}, filename:
     retval == 0 ||  error("Error parsing $filename: $(error_message(retval))")
 end
 
+function handle_write!(data::Ptr{UInt8}, len::Cint, ctx::Ptr)
+    io = unsafe_pointer_to_objref(ctx) # restore io
+    actual_data = unsafe_wrap(Array{UInt8}, data, (len, )) # we may want to specify the type later
+    write(io, actual_data)
+    return len
+ end
+
+function Writer(; filelabel)
+    writer = ccall((:readstat_writer_init, libreadstat), Ptr{Nothing}, ())
+    write_bytes = @cfunction(handle_write!, Cint, (Ptr{UInt8}, Cint, Ptr{Nothing}))
+    ccall((:readstat_set_data_writer, libreadstat), Int, (Ptr{Nothing}, Ptr{Nothing}), writer, write_bytes)
+    ccall((:readstat_writer_set_file_label, libreadstat), Cvoid, (Ptr{Nothing}, Cstring), writer, filelabel)
+    return writer
+end
+
+function write_data_file(filename::AbstractString, filetype::Val, source; kwargs...) 
+    io = open(filename, "w")
+    write_data_file(filetype::Val, io, source; kwargs...)
+    close(io)
+end
+
+
+function write_data_file(filetype::Val, io::IO, source; filelabel = "")
+    writer = Writer(; filelabel = filelabel)
+
+    rows = Tables.rows(source)
+    schema = Tables.schema(rows)
+    if schema === nothing
+        error("Could not determine table schema for data source.")
+    end
+    variables_array = []
+
+    variables_array = map(schema.names, schema.types) do column_name, column_type
+        readstat_type, storage_width = readstat_column_type_and_width(source, column_name, nonmissingtype(column_type))
+        return add_variable!(writer, column_name, readstat_type, storage_width)
+        # readstat_variable_set_label(variable, String(field)) TODO: label for a variable
+    end
+
+    readstat_begin_writing(writer, filetype, io, length(rows))
+
+    for row in rows
+        readstat_begin_row(writer)
+        Tables.eachcolumn(schema, row) do val, i, name
+            insert_value!(writer, variables_array[i], val)
+        end
+        readstat_end_row(writer);
+    end
+
+    ccall((:readstat_end_writing, libreadstat), Int, (Ptr{Nothing},), writer)
+    ccall((:readstat_writer_free, libreadstat), Cvoid, (Ptr{Nothing},), writer)
+end
+
+readstat_column_type_and_width(_, _, other_type) = error("Cannot handle column with element type $other_type. Is this type supported by ReadStat?")
+readstat_column_type_and_width(_, _, ::Type{Float64}) = READSTAT_TYPE_DOUBLE, 0
+readstat_column_type_and_width(_, _, ::Type{Float32}) = READSTAT_TYPE_FLOAT, 0
+readstat_column_type_and_width(_, _, ::Type{Int32}) = READSTAT_TYPE_INT32, 0
+readstat_column_type_and_width(_, _, ::Type{Int16}) = READSTAT_TYPE_INT16, 0
+readstat_column_type_and_width(_, _, ::Type{Int8}) = READSTAT_TYPE_CHAR, 0
+function readstat_column_type_and_width(source, colname, ::Type{String})
+    col = Tables.getcolumn(source, colname)
+    maxlen = maximum(col) do str
+        str === missing ? 0 : ncodeunits(str)
+    end
+    if maxlen >= 2045 # maximum length of normal strings
+        return READSTAT_TYPE_LONG_STRING, 0
+    else
+        return READSTAT_TYPE_STRING, maxlen
+    end
+end
+
+add_variable!(writer, name, type, width = 0) = readstat_add_variable(writer, name, type, width)
+
+insert_value!(writer, variable, value::Float64) = readstat_insert_double_value(writer, variable, value)
+insert_value!(writer, variable, value::Float32) = readstat_insert_float_value(writer, variable, value)
+insert_value!(writer, variable, ::Missing) = readstat_insert_missing_value(writer, variable)
+insert_value!(writer, variable, value::Int8) = readstat_insert_int8_value(writer, variable, value)
+insert_value!(writer, variable, value::Int16) = readstat_insert_int16_value(writer, variable, value)
+insert_value!(writer, variable, value::Int32) = readstat_insert_int32_value(writer, variable, value)
+insert_value!(writer, variable, value::AbstractString) = readstat_insert_string_value(writer, variable, value)
+
 read_dta(filename::AbstractString) = read_data_file(filename, Val(:dta))
 read_sav(filename::AbstractString) = read_data_file(filename, Val(:sav))
 read_por(filename::AbstractString) = read_data_file(filename, Val(:por))
 read_sas7bdat(filename::AbstractString) = read_data_file(filename, Val(:sas7bdat))
 read_xport(filename::AbstractString) = read_data_file(filename, Val(:xport))
 
+write_dta(filename::AbstractString, source; kwargs...) = write_data_file(filename, Val(:dta), source; kwargs...)
+write_sav(filename::AbstractString, source; kwargs...) = write_data_file(filename, Val(:sav), source; kwargs...)
+write_por(filename::AbstractString, source; kwargs...) = write_data_file(filename, Val(:por), source; kwargs...)
+write_sas7bdat(filename::AbstractString, source; kwargs...) = write_data_file(filename, Val(:sas7bdat), source; kwargs...)
+write_xport(filename::AbstractString, source; kwargs...) = write_data_file(filename, Val(:xport), source; kwargs...)
+
 end #module ReadStat
diff --git a/test/runtests.jl b/test/runtests.jl
index dbc10b0..09344fa 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -2,22 +2,75 @@ using ReadStat
 using DataValues
 using Test
 
-@testset "ReadStat: $ext files" for (reader, ext) in
-    ((read_dta, "dta"),
-     (read_sav, "sav"),
-     (read_sas7bdat, "sas7bdat"),
-     (read_xport, "xpt"))
-
-    dtafile = joinpath(dirname(@__FILE__), "types.$ext")
-    rsdf = reader(dtafile)
-    data = rsdf.data
-
-    @test length(data) == 6
-    @test rsdf.headers == [:vfloat, :vdouble, :vlong, :vint, :vbyte, :vstring]
-    @test data[1] == DataValueArray{Float32}([3.14, 7., NA])
-    @test data[2] == DataValueArray{Float64}([3.14, 7., NA])
-    @test data[3] == DataValueArray{Int32}([2, 7, NA])
-    @test data[4] == DataValueArray{Int16}([2, 7, NA])
-    @test data[5] == DataValueArray{Int8}([2, 7., NA])
-    @test data[6] == DataValueArray{String}(["2", "7", ""])
+testdir = joinpath(@__DIR__, "write_tests")
+if isdir(testdir)
+    rm(testdir, recursive = true)
+end
+mkdir(testdir)
+
+@testset "ReadStat" begin
+    @testset "$ext files" for (reader, writer, ext) in
+        ((read_dta, write_dta, "dta"),
+        (read_sav, write_sav, "sav"),
+        (read_sas7bdat, write_sas7bdat, "sas7bdat"),
+        (read_xport, write_xport, "xpt"))
+
+        @testset "Reading" begin
+            dtafile = joinpath(@__DIR__, "types.$ext")
+            rsdf = reader(dtafile)
+            data = rsdf.data
+
+            @test length(data) == 6
+            @test rsdf.headers == [:vfloat, :vdouble, :vlong, :vint, :vbyte, :vstring]
+            @test data[1] == DataValueArray{Float32}([3.14, 7., NA])
+            @test data[2] == DataValueArray{Float64}([3.14, 7., NA])
+            @test data[3] == DataValueArray{Int32}([2, 7, NA])
+            @test data[4] == DataValueArray{Int16}([2, 7, NA])
+            @test data[5] == DataValueArray{Int8}([2, 7., NA])
+            @test data[6] == DataValueArray{String}(["2", "7", ""])
+        end
+
+        @testset "Writing" begin
+            data = (
+                vdouble = [3.14, 7., missing],
+                vfloat = [3.14f0, 7.f0, missing],
+                vint32 = [Int32(2), Int32(7), missing],
+                vint16 = [Int16(2), Int16(7), missing],
+                vint8 = [Int8(2), Int8(7), missing],
+                vstring = ["2", "7", missing],
+            )
+            filepath = joinpath(testdir, "testwrite.$ext")
+            writer(filepath, data)
+            rsdf = reader(filepath)
+            data_read = rsdf.data
+            @test length(data_read) == length(data)
+            @test rsdf.headers == collect(keys(data))
+
+            same_value(a::DataValue, b) = a.hasvalue && get(a) == b # SAS and SPSS only support Float64 and String, so we can't test ===
+            same_value(a::DataValue, b::Missing) = !a.hasvalue
+            # missing String appears to be read back in as the empty string ""
+            same_value(a::DataValue{String}, b::Missing) = a.hasvalue && get(a) == ""
+        
+            @test all(zip(data_read, values(data))) do (col_read, col)
+                all(Base.splat(same_value), zip(col_read, col))
+            end
+        end
+
+        @testset "Long string" begin
+            data = (x = ["a" ^ 2046, missing],)
+            filepath = joinpath(testdir, "testwrite_longstring.$ext")
+            writer(filepath, data)
+            rsdf = reader(filepath)
+            data_read = rsdf.data
+            @test_broken get(data_read[1][1]) == "a" ^ 2046
+        end
+
+        @testset "File metadata" begin
+            data = (a = Int32[1, 2, 3],)
+            filepath = joinpath(testdir, "testwrite_file_metadata.$ext")
+            writer(filepath, data; filelabel = "Test label")
+            rsdf = reader(filepath)
+            @test rsdf.filelabel == "Test label"
+        end
+    end
 end