diff --git a/.github_changelog_generator b/.github_changelog_generator
index 8aeba8fbb1c..0d98d194cb8 100644
--- a/.github_changelog_generator
+++ b/.github_changelog_generator
@@ -1,7 +1,7 @@
-since-tag=v0.2.0
-future-release=v0.3.0
+since-tag=v0.3.0
+future-release=v0.4.0
 pr-wo-labels=false
-add-sections={"features":{"prefix":"**Enhancements:**","labels":["enhancement"]}, "documentation":{"prefix":"**Documentation updates:**","labels":["documentation"]}}
+add-sections={"features":{"prefix":"**Enhancements:**","labels":["enhancement"]}, "documentation":{"prefix":"**Documentation updates:**","labels":["documentation"]}, "testing":{"prefix":"**Testing updates:**","labels":["testing"]}}
 enhancement-label=**New features:**
 enhancement-labels=feature
 base=CHANGELOG.md
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0f3656d8f63..8ae11121211 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,77 @@
 # Changelog
 
+## [v0.4.0](https://github.com/jorgecarleitao/arrow2/tree/v0.4.0) (2021-08-24)
+
+[Full Changelog](https://github.com/jorgecarleitao/arrow2/compare/v0.3.0...v0.4.0)
+
+**Breaking changes:**
+
+- Change dictionary iterator of values from `Array`s of one element to `Scalar`s [\#335](https://github.com/jorgecarleitao/arrow2/issues/335)
+- Align FFI API with arrow's C++ API [\#328](https://github.com/jorgecarleitao/arrow2/issues/328)
+- Make `*_compare_scalar` not return `Result` [\#316](https://github.com/jorgecarleitao/arrow2/issues/316)
+- Make `io::print`, `get_value_display` and `get_display` not return `Result` [\#286](https://github.com/jorgecarleitao/arrow2/issues/286)
+- Add `MetadataVersion` to IPC interfaces [\#282](https://github.com/jorgecarleitao/arrow2/issues/282)
+- Change `DataType::Union` to enable round trips in IPC [\#281](https://github.com/jorgecarleitao/arrow2/issues/281)
+- Removed clone requirement in `StructArray -> RecordBatch` [\#307](https://github.com/jorgecarleitao/arrow2/pull/307) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Fixed error in reading a non-finished IPC stream. [\#302](https://github.com/jorgecarleitao/arrow2/pull/302) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Generalized ZipIterator to accept a `BitmapIter` [\#296](https://github.com/jorgecarleitao/arrow2/pull/296) ([jorgecarleitao](https://github.com/jorgecarleitao))
+
+**New features:**
+
+- Added API to FFI `Field` [\#321](https://github.com/jorgecarleitao/arrow2/pull/321) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Added `compare_scalar` [\#317](https://github.com/jorgecarleitao/arrow2/pull/317) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Add `UnionArray` [\#283](https://github.com/jorgecarleitao/arrow2/pull/283) ([jorgecarleitao](https://github.com/jorgecarleitao))
+
+**Fixed bugs:**
+
+- SliceIterator of last bytes is not correct [\#292](https://github.com/jorgecarleitao/arrow2/issues/292)
+- Fixed error in displaying dictionaries with nulls in values [\#334](https://github.com/jorgecarleitao/arrow2/pull/334) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Fixed error in dict equality [\#333](https://github.com/jorgecarleitao/arrow2/pull/333) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Fixed small inconsistencies between `compute::cast` and `compute::can_cast` [\#295](https://github.com/jorgecarleitao/arrow2/pull/295) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Removed order implementation for `days_ms` / `Interval(DayTime)` [\#285](https://github.com/jorgecarleitao/arrow2/pull/285) ([jorgecarleitao](https://github.com/jorgecarleitao))
+
+**Enhancements:**
+
+- Added support for remaining non-nested datatypes [\#336](https://github.com/jorgecarleitao/arrow2/pull/336) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Made `multiversion` and `lexical-core` optional [\#324](https://github.com/jorgecarleitao/arrow2/pull/324) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Improved performance of utf8 comparison \(1.7x-4x\) [\#322](https://github.com/jorgecarleitao/arrow2/pull/322) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Improved performance of boolean comparison \(5x-14x\) [\#318](https://github.com/jorgecarleitao/arrow2/pull/318) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Added trait `TryPush` [\#314](https://github.com/jorgecarleitao/arrow2/pull/314) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Added cast `date32 -> i64` and `date64 -> i32` [\#308](https://github.com/jorgecarleitao/arrow2/pull/308) ([ritchie46](https://github.com/ritchie46))
+- Improved performance of comparison with SIMD feature flag \(2x-3.5x\) [\#305](https://github.com/jorgecarleitao/arrow2/pull/305) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Added support to read json to `BinaryArray` [\#304](https://github.com/jorgecarleitao/arrow2/pull/304) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Improved `MutableFixedSizeBinaryArray` [\#303](https://github.com/jorgecarleitao/arrow2/pull/303) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Improved `MutablePrimitiveArray` and `MutableUtf8Array` [\#299](https://github.com/jorgecarleitao/arrow2/pull/299) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Improved `MutableBooleanArray` [\#297](https://github.com/jorgecarleitao/arrow2/pull/297) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Improved performance of concatenating non-aligned validities \(15x\) [\#291](https://github.com/jorgecarleitao/arrow2/pull/291) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Added support for timestamps with tz and interval to `io::print::write` [\#287](https://github.com/jorgecarleitao/arrow2/pull/287) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Improved debug repr of buffers and bitmaps. [\#284](https://github.com/jorgecarleitao/arrow2/pull/284) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Cleaned up internals of json integration [\#280](https://github.com/jorgecarleitao/arrow2/pull/280) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Removed `serde_derive` dependency [\#279](https://github.com/jorgecarleitao/arrow2/pull/279) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Simplified IPC code. [\#277](https://github.com/jorgecarleitao/arrow2/pull/277) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Reduced dependencies from confi-table and enabled `wasm` on `io_print` feature. [\#276](https://github.com/jorgecarleitao/arrow2/pull/276) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Improve performance of `rem_scalar/div_scalar` for integer types \(4x-10x\) [\#275](https://github.com/jorgecarleitao/arrow2/pull/275) ([ritchie46](https://github.com/ritchie46))
+
+**Documentation updates:**
+
+- Cleaned examples and docs from old API. [\#330](https://github.com/jorgecarleitao/arrow2/pull/330) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Improved documentation [\#306](https://github.com/jorgecarleitao/arrow2/pull/306) ([jorgecarleitao](https://github.com/jorgecarleitao))
+
+**Testing updates:**
+
+- Improved naming of testing workflows [\#315](https://github.com/jorgecarleitao/arrow2/pull/315) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Added tests to scalar API [\#300](https://github.com/jorgecarleitao/arrow2/pull/300) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Made CSV and JSON tests not use files. [\#290](https://github.com/jorgecarleitao/arrow2/pull/290) ([jorgecarleitao](https://github.com/jorgecarleitao))
+- Moved tests to integration tests [\#289](https://github.com/jorgecarleitao/arrow2/pull/289) ([jorgecarleitao](https://github.com/jorgecarleitao))
+
+**Closed issues:**
+
+- Make parquet\_read\_record support async [\#331](https://github.com/jorgecarleitao/arrow2/issues/331)
+- Panic due to SIMD comparison [\#312](https://github.com/jorgecarleitao/arrow2/issues/312)
+- Bitmap::mutable line 155 may Panic/segfault [\#309](https://github.com/jorgecarleitao/arrow2/issues/309)
+- IPC's `StreamReader` may abort due to excessive memory by overflowing a `usize`d variable [\#301](https://github.com/jorgecarleitao/arrow2/issues/301)
+- Improve performance of `rem_scalar/div_scalar` for integer types \(4x-10x\) [\#259](https://github.com/jorgecarleitao/arrow2/issues/259)
+
 ## [v0.3.0](https://github.com/jorgecarleitao/arrow2/tree/v0.3.0) (2021-08-11)
 
 [Full Changelog](https://github.com/jorgecarleitao/arrow2/compare/v0.2.0...v0.3.0)
diff --git a/Cargo.toml b/Cargo.toml
index 7175283b7cd..e057c40de6e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "arrow2"
-version = "0.3.0"
+version = "0.4.0"
 license = "Apache-2.0"
 description = "Unofficial implementation of Apache Arrow spec in safe Rust"
 homepage = "https://github.com/jorgecarleitao/arrow2"
diff --git a/README.md b/README.md
index 18b946ae63f..c739732b364 100644
--- a/README.md
+++ b/README.md
@@ -65,7 +65,7 @@ venv/bin/python parquet_integration/write_parquet.py
 * `MutableArray` API to work in-memory in-place.
 * faster IPC reader (different design that avoids an extra copy of all data)
 * IPC supports 2.0 (compression)
-* FFI support for dictionary-encoded arrays and union array
+* All implemented arrow types pass FFI integration tests against pyarrow / C++
 * All implemented arrow types pass IPC integration tests against other implementations
 
 ### Parquet