diff --git a/src/facet/facet_type.rs b/src/facet/facet_type.rs
new file mode 100644
index 000000000..13482e8b3
--- /dev/null
+++ b/src/facet/facet_type.rs
@@ -0,0 +1,15 @@
+use std::cmp;
+
+#[derive(Debug, Copy, Clone, PartialOrd, Ord, PartialEq, Eq, Hash)]
+pub enum FacetType {
+    String,
+    F64,
+    I64,
+    U64,
+}
+
+impl FacetType {
+    pub fn merge(a: FacetType, b: FacetType) -> FacetType {
+        cmp::min(a, b)
+    }
+}
diff --git a/src/facet/mod.rs b/src/facet/mod.rs
new file mode 100644
index 000000000..9ec99f2d3
--- /dev/null
+++ b/src/facet/mod.rs
@@ -0,0 +1,4 @@
+mod facet_type;
+pub mod value_encoding;
+
+pub use self::facet_type::FacetType;
diff --git a/src/facet/value_encoding.rs b/src/facet/value_encoding.rs
new file mode 100644
index 000000000..01fdba723
--- /dev/null
+++ b/src/facet/value_encoding.rs
@@ -0,0 +1,89 @@
+// https://stackoverflow.com/a/43305015/1941280
+#[inline]
+pub fn f64_into_bytes(float: f64) -> Option<[u8; 8]> {
+    if float.is_finite() {
+        if float == 0.0 || float == -0.0 {
+            return Some(xor_first_bit(0.0_f64.to_be_bytes()));
+        } else if float.is_sign_negative() {
+            return Some(xor_all_bits(float.to_be_bytes()));
+        } else if float.is_sign_positive() {
+            return Some(xor_first_bit(float.to_be_bytes()));
+        }
+    }
+    None
+}
+
+#[inline]
+pub fn u64_into_bytes(int: u64) -> [u8; 8] {
+    int.to_be_bytes()
+}
+
+#[inline]
+pub fn u64_from_bytes(bytes: [u8; 8]) -> u64 {
+    u64::from_be_bytes(bytes)
+}
+
+#[inline]
+pub fn i64_into_bytes(int: i64) -> [u8; 8] {
+    xor_first_bit(int.to_be_bytes())
+}
+
+#[inline]
+pub fn i64_from_bytes(bytes: [u8; 8]) -> i64 {
+    i64::from_be_bytes(xor_first_bit(bytes))
+}
+
+#[inline]
+fn xor_first_bit(mut x: [u8; 8]) -> [u8; 8] {
+    x[0] ^= 0x80;
+    x
+}
+
+#[inline]
+fn xor_all_bits(mut x: [u8; 8]) -> [u8; 8] {
+    x.iter_mut().for_each(|b| *b ^= 0xff);
+    x
+}
+
+#[cfg(test)]
+mod tests {
+    use std::cmp::Ordering::Less;
+    use super::*;
+
+    fn is_sorted<T: Ord>(x: &[T]) -> bool {
+        x.windows(2).map(|x| x[0].cmp(&x[1])).all(|o| o == Less)
+    }
+
+    #[test]
+    fn ordered_f64_bytes() {
+        let a = -13_f64;
+        let b = -10.0;
+        let c = -0.0;
+        let d =  1.0;
+        let e =  43.0;
+
+        let vec: Vec<_> = [a, b, c, d, e].iter().cloned().map(f64_into_bytes).collect();
+        assert!(is_sorted(&vec), "{:?}", vec);
+    }
+
+    #[test]
+    fn ordered_u64_bytes() {
+        let a = 0_u64;
+        let b = 1_u64;
+        let c = 43_u64;
+
+        let vec: Vec<_> = [a, b, c].iter().cloned().map(u64_into_bytes).collect();
+        assert!(is_sorted(&vec), "{:?}", vec);
+    }
+
+    #[test]
+    fn ordered_i64_bytes() {
+        let a = -10_i64;
+        let b = -0_i64;
+        let c =  1_i64;
+        let d =  43_i64;
+
+        let vec: Vec<_> = [a, b, c, d].iter().cloned().map(i64_into_bytes).collect();
+        assert!(is_sorted(&vec), "{:?}", vec);
+    }
+}
diff --git a/src/heed_codec/facet/facet_value_f64_codec.rs b/src/heed_codec/facet/facet_value_f64_codec.rs
new file mode 100644
index 000000000..fdacb1f08
--- /dev/null
+++ b/src/heed_codec/facet/facet_value_f64_codec.rs
@@ -0,0 +1,50 @@
+use std::borrow::Cow;
+use std::convert::TryInto;
+use std::str;
+
+use crate::heed_codec::StrBytesCodec;
+use crate::facet::value_encoding::f64_into_bytes;
+
+pub struct FacetValueF64Codec;
+
+impl<'a> heed::BytesDecode<'a> for FacetValueF64Codec {
+    type DItem = (&'a str, f64);
+
+    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+        let (name, buffer) = StrBytesCodec::bytes_decode(bytes)?;
+        let value = buffer[8..].try_into().ok().map(f64::from_be_bytes)?;
+        Some((name, value))
+    }
+}
+
+impl<'a> heed::BytesEncode<'a> for FacetValueF64Codec {
+    type EItem = (&'a str, f64);
+
+    fn bytes_encode((name, value): &Self::EItem) -> Option<Cow<[u8]>> {
+        let mut buffer = [0u8; 16];
+
+        // Write the globally ordered float.
+        let bytes = f64_into_bytes(*value)?;
+        buffer[..8].copy_from_slice(&bytes[..]);
+
+        // Then the f64 value just to be able to read it back.
+        let bytes = value.to_be_bytes();
+        buffer[8..].copy_from_slice(&bytes[..]);
+
+        let tuple = (*name, &buffer[..]);
+        StrBytesCodec::bytes_encode(&tuple).map(Cow::into_owned).map(Cow::Owned)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use heed::{BytesEncode, BytesDecode};
+    use super::*;
+
+    #[test]
+    fn globally_ordered_f64() {
+        let bytes = FacetValueF64Codec::bytes_encode(&("hello", -32.0)).unwrap();
+        let (name, value) = FacetValueF64Codec::bytes_decode(&bytes).unwrap();
+        assert_eq!((name, value), ("hello", -32.0));
+    }
+}
diff --git a/src/heed_codec/facet/facet_value_i64_codec.rs b/src/heed_codec/facet/facet_value_i64_codec.rs
new file mode 100644
index 000000000..e3c333883
--- /dev/null
+++ b/src/heed_codec/facet/facet_value_i64_codec.rs
@@ -0,0 +1,28 @@
+use std::borrow::Cow;
+use std::convert::TryInto;
+use std::str;
+
+use crate::heed_codec::StrBytesCodec;
+use crate::facet::value_encoding::{i64_from_bytes, i64_into_bytes};
+
+pub struct FacetValueI64Codec;
+
+impl<'a> heed::BytesDecode<'a> for FacetValueI64Codec {
+    type DItem = (&'a str, i64);
+
+    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+        let (name, bytes) = StrBytesCodec::bytes_decode(bytes)?;
+        let value = bytes.try_into().map(i64_from_bytes).ok()?;
+        Some((name, value))
+    }
+}
+
+impl<'a> heed::BytesEncode<'a> for FacetValueI64Codec {
+    type EItem = (&'a str, i64);
+
+    fn bytes_encode((name, value): &Self::EItem) -> Option<Cow<[u8]>> {
+        let value = i64_into_bytes(*value);
+        let tuple = (*name, &value[..]);
+        StrBytesCodec::bytes_encode(&tuple).map(Cow::into_owned).map(Cow::Owned)
+    }
+}
diff --git a/src/heed_codec/facet/facet_value_string_codec.rs b/src/heed_codec/facet/facet_value_string_codec.rs
new file mode 100644
index 000000000..8b046192a
--- /dev/null
+++ b/src/heed_codec/facet/facet_value_string_codec.rs
@@ -0,0 +1,25 @@
+use std::borrow::Cow;
+use std::str;
+
+use crate::heed_codec::StrBytesCodec;
+
+pub struct FacetValueStringCodec;
+
+impl<'a> heed::BytesDecode<'a> for FacetValueStringCodec {
+    type DItem = (&'a str, &'a str);
+
+    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+        let (name, bytes) = StrBytesCodec::bytes_decode(bytes)?;
+        let value = str::from_utf8(bytes).ok()?;
+        Some((name, value))
+    }
+}
+
+impl<'a> heed::BytesEncode<'a> for FacetValueStringCodec {
+    type EItem = (&'a str, &'a str);
+
+    fn bytes_encode((name, value): &Self::EItem) -> Option<Cow<[u8]>> {
+        let tuple = (*name, value.as_bytes());
+        StrBytesCodec::bytes_encode(&tuple).map(Cow::into_owned).map(Cow::Owned)
+    }
+}
diff --git a/src/heed_codec/facet/facet_value_u64_codec.rs b/src/heed_codec/facet/facet_value_u64_codec.rs
new file mode 100644
index 000000000..2fdc7416e
--- /dev/null
+++ b/src/heed_codec/facet/facet_value_u64_codec.rs
@@ -0,0 +1,28 @@
+use std::borrow::Cow;
+use std::convert::TryInto;
+use std::str;
+
+use crate::heed_codec::StrBytesCodec;
+use crate::facet::value_encoding::{u64_from_bytes, u64_into_bytes};
+
+pub struct FacetValueU64Codec;
+
+impl<'a> heed::BytesDecode<'a> for FacetValueU64Codec {
+    type DItem = (&'a str, u64);
+
+    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+        let (name, bytes) = StrBytesCodec::bytes_decode(bytes)?;
+        let value = bytes.try_into().map(u64_from_bytes).ok()?;
+        Some((name, value))
+    }
+}
+
+impl<'a> heed::BytesEncode<'a> for FacetValueU64Codec {
+    type EItem = (&'a str, u64);
+
+    fn bytes_encode((name, value): &Self::EItem) -> Option<Cow<[u8]>> {
+        let value = u64_into_bytes(*value);
+        let tuple = (*name, &value[..]);
+        StrBytesCodec::bytes_encode(&tuple).map(Cow::into_owned).map(Cow::Owned)
+    }
+}
diff --git a/src/heed_codec/facet/mod.rs b/src/heed_codec/facet/mod.rs
new file mode 100644
index 000000000..ba34f6220
--- /dev/null
+++ b/src/heed_codec/facet/mod.rs
@@ -0,0 +1,9 @@
+mod facet_value_f64_codec;
+mod facet_value_i64_codec;
+mod facet_value_string_codec;
+mod facet_value_u64_codec;
+
+pub use self::facet_value_f64_codec::FacetValueF64Codec;
+pub use self::facet_value_i64_codec::FacetValueI64Codec;
+pub use self::facet_value_string_codec::FacetValueStringCodec;
+pub use self::facet_value_u64_codec::FacetValueU64Codec;
diff --git a/src/heed_codec/mod.rs b/src/heed_codec/mod.rs
index 68739fbf1..260e79c4b 100644
--- a/src/heed_codec/mod.rs
+++ b/src/heed_codec/mod.rs
@@ -1,8 +1,10 @@
 mod beu32_str_codec;
 mod bo_roaring_bitmap_codec;
 mod cbo_roaring_bitmap_codec;
+mod facet;
 mod obkv_codec;
 mod roaring_bitmap_codec;
+mod str_bytes_codec;
 mod str_str_u8_codec;
 
 pub use self::beu32_str_codec::BEU32StrCodec;
@@ -10,4 +12,5 @@ pub use self::bo_roaring_bitmap_codec::BoRoaringBitmapCodec;
 pub use self::cbo_roaring_bitmap_codec::CboRoaringBitmapCodec;
 pub use self::obkv_codec::ObkvCodec;
 pub use self::roaring_bitmap_codec::RoaringBitmapCodec;
+pub use self::str_bytes_codec::StrBytesCodec;
 pub use self::str_str_u8_codec::StrStrU8Codec;
diff --git a/src/heed_codec/str_bytes_codec.rs b/src/heed_codec/str_bytes_codec.rs
new file mode 100644
index 000000000..1a864c1fb
--- /dev/null
+++ b/src/heed_codec/str_bytes_codec.rs
@@ -0,0 +1,28 @@
+use std::borrow::Cow;
+use std::str;
+
+pub struct StrBytesCodec;
+
+impl<'a> heed::BytesDecode<'a> for StrBytesCodec {
+    type DItem = (&'a str, &'a [u8]);
+
+    fn bytes_decode(bytes: &'a [u8]) -> Option<Self::DItem> {
+        let s1_end = bytes.iter().position(|b| *b == 0)?;
+        let (s1_bytes, s2_bytes) = bytes.split_at(s1_end);
+        let s1 = str::from_utf8(s1_bytes).ok()?;
+        let s2 = &s2_bytes[1..];
+        Some((s1, s2))
+    }
+}
+
+impl<'a> heed::BytesEncode<'a> for StrBytesCodec {
+    type EItem = (&'a str, &'a [u8]);
+
+    fn bytes_encode((s1, s2): &Self::EItem) -> Option<Cow<[u8]>> {
+        let mut bytes = Vec::with_capacity(s1.len() + s2.len() + 1);
+        bytes.extend_from_slice(s1.as_bytes());
+        bytes.push(0);
+        bytes.extend_from_slice(s2);
+        Some(Cow::Owned(bytes))
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index bea05e68a..2e879fd03 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -4,6 +4,7 @@ mod index;
 mod mdfs;
 mod query_tokens;
 mod search;
+pub mod facet;
 pub mod heed_codec;
 pub mod proximity;
 pub mod subcommand;